Seriously, he's a putz
Thinking about it, Yoshi is quite the d*ck. Whenever you get knocked off, he just runs away without a care in the world. This video by Busted Pixel is all the proof you need.
Then again, Mario does use Yoshi as a stepping stone to cross wide chasms, letting the poor dino fall to his death. I guess it's karma.
Busted Pixel: Yoshi [YouTube]