Honestly they should've started doing that at the launch of the Wii U. Maybe COD and Splinter Cell Blacklist wouldn't million sellers, but they would've sold more, especially Blacklist (seriously, why did no one buy that).

They don't - the not hardcore (aka not following gaming ones like all of us here) basically don't know.

They can't because Nintendo fans mainly like Nintendo franchises.

And for the few Nintendo fans who also enjoy third party titles, well they probably bought a PS4, or gaming PC to play those titles as those platforms have a much larger competitive online community. 

The problem is the opposite, it's the fanbase of most 3rd party games who aren't interested in WiiU.

Although Wii U fans have bought 3rd party games in small numbers, some of the blame has to be from the 3rd parties themselves and not just Nintendo. I mean, something like COD is barely advertised being on Wii U, then some games dont get parity with the other versions ie missing features, no online, no DLC etc. If 3rd parties wanted to sell their games on Wii U then they could have tried harder to make more people aware of them. Black ops 2 on Wii U has the unique ability to play co-op with a friend without the need for split screen, a great ad for the gamepad, but you barely know them game exists nevermind that additional cool feature.

Then explain why nobody bought ACIV? It was a great game, released at the same time as the 360 and PS3 versions, hell it released well before the PS4 and XBO versions, yet it still sold incredibly poorly.

Then all you really need is a wii u

Nintendo would have to radically change their approach to hardware and the culture of their fandom in order to match Sony and Microsoft in the quest for third-party support.

In regards to hardware, Nintendo would need to start catching up, instead of staying a gen behind as they have done with the Wii and Wii U. At the same time, they would have to sell enough units to keep up decently with the competition.

However, there is a culture problem as well. Some of Nintendo's fans are simply a casual crowd who don't really have interest in much more than Mario, Just Dance, etc. As for the Nintendo hardcore, a lot of them live entirely or mostly in a "Nintendo bubble," if you will, where they tend to stick with Nintendo franchises and tailor their gaming tastes based on that. These people are not inclined to buy third-party titles even when Nintendo platforms do get them.

Because their handhelds don't have as significant a culture problem and because the handheld market isn't very multiplatform-oriented, we find that Nintendo's handhelds do better in this regard than their consoles do.

I think he already explained it 

Simple Nintendo's bad image. When a game does atually come out on time, and has 0 missing features etc. Nintendo is also fucked because of the auto response people do: "This is nerfed somehow, SKIP." Nintendo needs to stop this programed mindset. I'll totally admit I've done this before. I've assumed The armor edition of Batman on Wii U was total crap. I though the extra functions that they gave the pad were pointless and not worth rebuying the game for. But I did no research on the game. It probably is good. but I never cared to give it a chance.