Retail chains would probably love to only have one (or maybe two) consoles that they could concentrate their limited shelf-space on. So far Wii U has, despite its total failure in sales and marketing, defended its right to exist as a choice in most chains. This way they still will exist in the minds of the consumers (even if they do not buy Wii U). This will be good for the next generation: to have the sales channels, the brand recognition, the market presence. To loose all of this entirely and build it up again is immensely expensive and time consumeing.
All the people that once enjoyed the Wii and associated this with Nintendo will easier return and buy the next good thing (NX) that comes from Ninendo if they can come trough this generation without loosing their market presence.

there's a number of reasons why it hasn't:

no one (relatively speaking) knows about the wii u.
people who've bought one actually like the gimmicky controller.

if people who'd bought one all said they hated it and through it in the trash, it'd be different.

Now...who got metacritic's publisher of the year last year? and which companies got ripped apart for releasing incomplete, overpriced, buggy, unoriginal games?

Not really.

Their image started to change ever since the N64.

I don't know. I can see being upset by the lack of game releases (AKA droughts) but this gen with Nintendo has offered a LOT. If it has done anything (IMO) it has shown Nintendo is opening their doors to some M rated games I never thought they would go for (Bayo as an exclusive has blown my mind) and am optimistic about the future because of it. There are several ways they could get third parties back, and I think this gen will be the bridge to whatever way they decide to go with it next gen.

Nintendo has M-rated exclusives every generation.

N64-Perfect Dark, Conker, Turok

GC-Resident Evil, Eternal Darkness

Wii-Madworld, Fatal Frame

True, very true though Fatal Frame is a teen rated I believe. But they never personally sought these types of games out and funded them (after N64 era).  A decade is a long time to never (themselves) really push mature rated titles (but more they allowed devs to publish them). 

Fatal Frame is M, it was published by Nintendo and I believe they may even co-own the series now (might be wrong about that). They also own Eternal Darkness and the Resident Evil exclusivity was part of a Nintendo/Capcom deal called the Capcom 5 so Nintendo has certainly sought and funded these M-rated games post N64-era.

Not at all. You just need to play the gams on it to see its a great machine.

Well I won't be buying any more Nintendo hardware unless things drastically change. Nintendo seem to be pulling back from supporting the Wii U rather than getting behind it in its time of need.

Well Project Zero 2 was rated 16

and Zero IV Mask Of The Lunar Eclipe was rated Cero C (15+) in Japan...

http://fatalframe.wikia.com/wiki/Fatal_Frame_IV:_Mask_of_the_Lunar_Eclipse

so neither of these titles were M. We also have to remember any Nintendo published Fatal Frames were not released worldwide yet... Except for the Wii U one. *Edit* For the record Zero V is rated Cero D (17+ or M rated). So they are even upping the rating on some of their already established franchises. Another solid point for Nintendo supporting M rated titles.

Eternal Darkness and RE I give you. I can't really point out any real marketing for Eternal Darkness though. Fatal Frame V seems like it is getting a HUGE backing from TK and Nintendo, as did Bayo.