This. I still buy more first party games, but I buy way more 3rd party on the 3DS. I'd buy a new Street Fighter on the Wii U with no second thought. If I didn't have REvelations 3DS, I'd love that on the Wii U. 

because nintendo games are better.
multis are also cheaper and complete in other platforms.

Third party multi-plats aren't the games most people buy the Wii U for or almost any other Nintendo console. A game like Call of Duty is usually best associated with Xbox or PS because they sell a crapload of copies on those consoles.

because they like 1st party

Because my experiences with 3rd party games has more often than not left me with a bitter taste.

If 3rd parties won't step it up, they won't get rewarded.

Rayman Legends was the result of a concerted boycott and subsequent malaise, and Ubisoft rightfully earned that treatment.

I don't buy 3rd party games generally because I find most of them boring. If I wanted those kinds of games I'd buy an XBoxOne or PS4. Meh.

That being said, my favorite game on the WiiU is a 3rd party game: Lego City Undercover.  There's always exceptions. 

I have 19 3rd party games on my Wii U, but Nintendo games rule and will always be a priority purchase for me.

because the devs dont support the games that they release on wii u

Man, people are so wrong in this thread.

Various reasons.

1. Most are weaker than ps3/360 except for racing games and 2D games
2. I own a PC and 360 and PS3 so have other options to buy games
3. I prefer the 360 and PS3 controllers for most types of games
4. My AV amp only supports optical or coaxial input so no surround sound if I buy the wii u version
5. wii u games are often slower loading which is annoying
6. If I'm buying a downloadable game I prefer to use steam or psn
7. wii u versions seem to commonly miss out some features
8. No analogue triggers on gamepad which benefit many games
9. short battery life of gamepad means often more convenient to play on ps3, pc or 360
10. some wii u games become unplayable when there is a lot of action on screen and the frame rate drops considerably more than 360 or ps3