Say what you want about Turbo, but winning was just in his code, like being a racer was in Vanellope's. I'm not saying this justifies what he did (ostracizing an unsuspecting little girl and, if you want to get technical about what he did to his fellow racers and the guys from RoadBlasters, murder), but, when he stopped being so popular and the kids that loved him so much flocked over to the new "advanced" racing game, that had to have hurt. Eaten away at him. Made him snap.
Granted he could've handled it better, when all he knows is racing and winning - and got to do neither as less and less kids played - what else do you expect to happen?
Disclaimer: I own nothing.
Turbo's the name
Winning is a must
Racing's the game
First place or bust
He can't cope with second place
He simply can't lose
A game-jumping disgrace
The path he did choose
Being first is simply a part of his code
When it was no longer his time to shine,
It caused him to unfold
It caused him to unwind
In a dark, brooding mood,
A disastrous plan filled the space
Crash the RoadBlaster dudes
And reclaim his rightful place
As the greatest racer ever
As the star of the arcade
It was a plan quite clever
Too bad it had decayed
Both games were unplugged
Everyone thought he was a goner
His reputation snubbed
Such a dishonor
But he would prove them all wrong
He would rise again
He had fooled them all along
A monster deep within