Earlier quoted context omitted.
Lagging in specs is a major reason 3rd parties shun Nintendo's consoles. Porting a game between XB1, PS4 and PC is relatively easy due to them all being of similar caliber. But the cutbacks required for porting to Wii U usually means they just don't bother.
I'd say it has more to do with demographics than specs. Nintendo's demographics usually only buy first party titles, and Nintendo hasn't done much to market themselves towards the xbox/ps demographics. If they're paying devs to have Skyrim/NBA on their consoles, that's a good first step, and hopefully a sign of things to come.
The SNES had extensive 3rd party support. Obviously it's hard to compare 25 years ago to today, but the SNES and Genesis were really "even". Supporting both systems was a no brainer for most game companies. The N64 threw a curve ball with carts, and 3rd party support tanked. Anecdotally, the GameCube seemed to have better 3rd party support, as it was a very equivalent system to the Xbox and PS2.