I was watching this doc about why Tim Burton's Superman Lives movie wasn't made. Warner Bros. had lost a lot of money in 1998 and wouldn't risk going against the grain on such an ambitious take on Superman, because Hollywood doesn't like changing their formulaic way of thinking. I think WWE has the same problem. Instead of taking a risk putting the title on Cesaro, they'd rather go with what they're used to in putting the belt on a guy like Cena or someone similar who fits Vince's idea of a superstar. Not to say that Roman isn't deserving but they fukked up not letting him win last year at Mania.
I agree to a degree, but then I can also kind of see how the WWE may think. A long time ago, the people wanted Rocky Maivia off their TV screen and he went on to elevate the entire product as we know it. They give people who they want and a lot of times, they end up becoming liabilities:
Make Daniel Bryan the man: Gone a year later
Make Seth Rollins the man: About to miss precious time
Make Cena the man and he's not missing the money-makers and he's numbers stay afloat.
They're probably afraid to invest too hard into someone whose body is a liability (Bryan, Michaels) or don't strike them as a company guy that wouldn't walk out. (a la Bret, Punk)
The want more Undertakers and Cenas to keep the company going.