I went into a bit more detail in my response to Soundwave.

On DS, Nintendogs, Mario Kart, Animal Crossing, Brain Age, NSMB, all released back to back to back within an 8-9 months span. None of these games individually would have done a ton for DS but having them all release one right after another like they did from August 2005-May 2006 caused a huge increase in casual interest and Nintendo & 3rd parties continued to provide strong support for this market for the next few years.

This never happened on 3DS, Nintendogs+Cats released at launch in March 2011 but that one game can only do so much by itself, games like Style Savvy, Art Academy, Brain Age all released in late 2012/early 2013, which is 1.5-2 years later. There wasnt realy any notable casual software released between March 2011 & September 2012. 3D Land/Mario Kart are casual-core and they released 8-9 months after Nintendogs and NSMB2 released another 8-9 months after that.

This same thing applies to Wii/Wii U. Wii had big casual games right out of the gate and these type of games really never stopped coming for the first few years. Wii U on the other hand had the big NSMBU+Nintendo Land combo but pretty much nothing else for a year when a few released during holiday 2013, another case of too little, too late.

Software output isn't the only problem, 3DS/Wii U both cost $100 more than DS/Wii at launch, both had consumer confusion issues, 3DS was thought to be a DS revision with a 3D screen, Wii U was thought to be a tablet accessory for Wii, when retailers have to make signs telling consumers that these are in fact new devices than u know u fucked up the design & marketing.

Software output+poor hardware design+poor marketing+high price for what device offers is what killed the casual market on Nintendo devices. Of course mobile contributed greatly and a decline likely would have happened regardless but Nintendo could have had a much better showing without making so many mistakes.

It's not necessarily that Nintendo underestimated mobile, it's more like there simply wasn't a big mobile presence when R&D for 3DS/Wii U was happening. iOS released in 2007 along with Android in 2008 and the gaming scene on both took awhile to take off. I think 2010 was the year mobile gaming really started to get bug and by that point 3DS was just about to be released and Wii U about to be unveiled so by that point it was too late to react and adapt.

Or if they delay a full year to release on the next system, like what happened with TP, it will be Nintendo's failure and not only the team.

Certain series showed declines but overall annual software sales were pretty consistent in 2008-2010 and didn't show any really notable declines until 2011.

2007

DS-110m, Wii-75m, total-185m

2008

DS-155m, Wii-177m, total-332m

2009

DS-144m, Wii-182m, total-326m

2010

DS-121m, Wii-182m, total-303m

2011

DS-81m, Wii-135m, total-216m

Perhaps it comes down to most casuals on DS/Wii didn't want or need more than 1-2 entries of each franchise or had enough games in that particular genre. If somebody owned Wii Sports, Wii Play, Carnival Games, Mario Party 8, Deca Sports, Mario & Sonic Olympics, maybe that's enough mini game compilations for them for a few years. Or if somebody owned Wii Fit, Wii Fit Plus, Zumba Fitness, 2-3 Just Dance games than they are probably set on fitness/dance games for awhile.

We kinda see this on mobile as well, Angry Birds & Candy Crush Saga sequels & spinoffs have not been downloaded nearly as much as the originals despite being free. Just because Call of Duty & sports games get annual releases and don't see a major decline doesn't mean that formula works for other games. There is probably a reason why Nintendo only releases 1-2 entries of any franchise per generation.

We saw a lot of 3rd parties use the "let's milk this for all its worth before it dries up!!!" mentality by pumping out shit game after shit game on Wii & DS, that could be another reason as well. Just because someone is a casual gamer doesn't mean they don't enjoy quality games.

Certain series showed declines but overall annual software sales were pretty consistent in 2008-2010 and didn't show any really notable declines until 2011.

2007

DS-110m, Wii-75m, total-185m

2008

DS-155m, Wii-177m, total-332m

2009

DS-144m, Wii-182m, total-326m

2010

DS-121m, Wii-182m, total-303m

2011

DS-81m, Wii-135m, total-216m

Perhaps it comes down to most casuals on DS/Wii didn't want or need more than 1-2 entries of each franchise or had enough games in that particular genre. If somebody owned Wii Sports, Wii Play, Carnival Games, Mario Party 8, Deca Sports, Mario & Sonic Olympics, maybe that's enough mini game compilations for them for a few years. Or if somebody owned Wii Fit, Wii Fit Plus, Zumba Fitness, 2-3 Just Dance games than they are probably set on fitness/dance games for awhile.

We kinda see this on mobile as well, Angry Birds & Candy Crush Saga sequels & spinoffs have not been downloaded nearly as much as the originals despite being free. Just because Call of Duty & sports games get annual releases and don't see a major decline doesn't mean that formula works for other games. There is probably a reason why Nintendo only releases 1-2 entries of any franchise per generation.

We saw a lot of 3rd parties use the "let's milk this for all its worth before it dries up!!!" mentality by pumping out shit game after shit game on Wii & DS, that could be another reason as well. Just because someone is a casual gamer doesn't mean they don't enjoy quality games.

Thank you for acknowledging the latter point though. Casual gaming is its own market with its own quirks to it. But that point also illustrates why it's very hard for Nintendo to keep casuals. 

Just because they made Wii Sports and Wii Fit didn't mean anything to casuals once they get tired of that type of game. It's all about what do you have today and repeating on casual success is very difficult. Nintendo could not do it with Wii Music and Nintendo Land. 

And yes absolutely we see this continue on mobile too, makers of blockbusters like Angry Birds and Candy Crush are having trouble finding that next big hit. 

The casual market is like the pop music market ... just because you have a pop music hit, doesn't mean the audience is going to like that same song or artist forever, the audience is fickle in what they like. 

Hardcore gamers are different (I'm not saying better, just different) in the sense that once they like something they tend to like it for a looooooong ass time. Franchises like GTA, Zelda, Street Fighter, Call of Duty, Mario, Madden, Pokemon, have fanbases that now span multiple decades. 

Exactly. Guitar Hero/Rock Band would be other examples too. Brain Training collapsed hillariously too, like from 20 million to 90,000. 

It's not bad to admit casual gaming is largely driven by fads ... there's nothing wrong with that. Fads are fun for their time. I bumped the hell out of Gangam Style that one summer, but would I don't have much interest in hearing that song again or buying a new Psy album or any kind of Korean pop. 

Casual gamers are a different breed, they like something, they play the hell out of it for a while, then they get bored of it and want something completely different. 

Think about which casual franchise has had any longevity? Wii Sports? Nope. Wii Fit? Nope. Guitar Hero? Nope. Brain Age? Nope. Nintendogs? Nope. Kinect Sports? Nope. Even on mobile ... Angry Birds? Nope. Clash of Clans and Candy Crush are going strong now but will fizzle out eventually. Just Dance does well but it's way down too (10 million a few years ago, down to 2 million, which is actually quite impressive but still a massive fall off).