Mass Effect is not open world at all and only 3 had multiplayer. The rest may have had multiplayer modes but the marketing focus has been pre-dominantly on single-player which is quite telling. The PS4 Uncharted remakes aren't even shipping with the multiplayer modes.

Dishonored sold well-enough to warrant a sequel and exceed expectations at Bethesda. I remember reading it was around 2.5 million physical sales a couple of years ago which isn't too shabby for a new IP. 

Also, Wolfenstein: The New Order, Metro 2033/Last Light, The Walking Dead, Life is Strange, Final Fantasy (although I hated XIII it still sold well) and most Mario games... you get the idea

I think we can all agree that it's a good thing that you are not in charge of a major publisher. It's a pretty good thing most of the industry seems to disagree with you.

No, I don't get the idea why you would use big existing franchises like Final Fantasy or Mario or even a big IP like The Walking Dead.

I cannot find sales data for Dishonored but a sequel doesn't mean it did well - the decs might just want to re-use the assets and tech.

Did those other games sell well by multiplatform standards? I can't say.

1. Well by that logic we shouldn't include big IPs like Battlefield for multiplayer or Skyrim for sandbox. If we only look at new IPs from relatively unknown developers it's not like the sales are particularly different for single-player, multiplayer or sandbox. These IPs became big for a reason.

2. Sales info for Dishonored:

"Dishonored came out last year from Bethesda. It had a very modest budget with almost no expected sales for revenue (I think the profit turn around was just 800k in sales). They moved 2.45 million units, and that's only counting physical product."

http://www.gamnesia.com/articles/why-cant-3.4-million-in-sales-be-profitable-for-a-game

and it exceeded expectations:

http://www.engadget.com/2012/11/28/dishonored-sales-exceed-bethesdas-expectations/

3. Wolfenstein sold 2.27 million (physical) on consoles, including PC and digital it's probably around 3 million.

The remake of the Metro games sold 1.5 million (http://www.gamespot.com/articles/metro-redux-sells-1-5-million-copies/1100-6426640/), the full sales will be higher, but also the costs of these games was relatively low for AAA titles so the profits would have been very high. 

Life is Strange has broken 1 million which is very impressive for a relatively low budget download-only title that's also a new IP (http://metro.co.uk/2015/07/23/life-is-strange-hits-1-million-sales-episode-4-out-next-tuesday-5309455/). 

Walking Dead sold 21 million episodes from season 1 alone as of 2013 (http://www.engadget.com/2013/10/29/walking-dead-goty-edition-official-over-21-million-episodes-sol/).

1. The industry has changed a lot since the days when a lot of those big IPs were created. It changed a lot since the first couple of years of Ben 7. If you look at the best selling new IPs, they're either open-world games or multiplayer games.

2. Not sure where that Dishonored sales data comes from but I can't see it being used anywhere else.

3. Are those numbers a lot for Multiplatform games? Seems about par for the course to me.

And The Walking Dead is a big IP before the games came out. And 21M episodes is 4.2M per episode across console, PC, hanheld and mobile I believe.

And Life is Strange - is that 1M for all the episodes across all 5 systems?

To hell with multiplayer. Give me a good story to enjoy.

The MMO market is limited, CoD sells well, ye it does but it eats the avaliable market for that genre of MP, you have very few other shooters that can come close to its numbers cause of that/ WoW is a jugernault, but most other MMO RPGs strugle to have even 100k subs since everyone is on WoW (and lately FF XIV as well). Players tend to flock to one MMO game and the others all crash and burn. So realy the industry wont focus more than they already focus on this market in the future.

But without the multiplayer, the game wouldn't have sold half of what it did. The OP has a point. I've been gaming longer than 99% of the people on this forum, before most of them were alive and I've watched the industry become one big "no MP? no purchase" jerk fest. 

I'm not saying single player is going to die off, but it's obvious that it's a now a shell of it's former self. The amount of people like myself that enjoy it is shrinking every generation.

The revenue is there for multiplayer games. Look at the amount of money LOL and CS:go bring in, or the amount Activision/Blizzard brings in for its franchises compared to single player games. MMO, free to play, and mobile digital games are killing it.

Of course you will never have the popularity or the reach like e-sports will have with single player, because nobody is interested in seeing fat loser neckbeards badly play through single player games. Beating a single player game isn't as great or as exciting as fighting for the top prize against other real live competitors. The top channels on twitch are all multiplayer games.

Yeah... Single player games are doing just fine.

Also, there's such a thing as market saturation; there'd be far more bombs if everyone was focused on multiplayer games.

Oh, and one thing you failed to consider is that the average age of gamers is rising, not dropping, and the 18+ crowd is very much larger than the young'ns. What we're seeing is that, while there is some fall off, a great many people simply don't stop playing games as they age.