There are many reasons why a WWE superstar otherwise deserving of the sort of push that'd have Jurassic Park's Dr. Hammond aflutter with excitement might not receive one, and they pretty much all come down to spite or personal animosity.
A host of wrestlers arriving from rival organisations quickly found their prospects limited upon arrival, even if they'd previously been their territory's top draw. Dusty Rhodes was slapped in polka dots and lumbered with a useless albeit endearing manager. DDP went from smiling man of the people - someone whose popularity rose above the nWo malaise - to a grimacing stalker, beaten clean by a woman with no previous wrestling experience and made to look a complete chump. Wisely, Sting rejected the company's overtures until the point when his intact legacy simply could not be diminished - though WWE tried their hardest in his one and only WrestleMania match.
Success with a competitor is a petty reason to undermine your own talent, but it's not necessarily stupid. Not like, for example, holding the finest technical wrestler of his generation back because he doesn't eat steak.
And such acts of booking stupidity aren't as rare as you think. They're not even medium rare.