One of the most important decisions a wrestling booker faces in their daily work is whether a given performer should be a face or a heel.
Imagine if Stone Cold Steve Austin hadn't become a good guy in 1997, for instance. WWF might never have kick-started the Attitude Era, instead losing the Monday Night Wars to ratings rivals WCW, and in turn going out of business in the early 2000s (granted, that's worst case scenario - and was never actually likely).
Here's a more recent example: imagine if WWE had spent the last three years trying to push a man who the fans absolute loathe as their next franchise player, passing up a number of presentable opportunities to turn him heel because of sheer, wrong-headed stubbornness on the part of their chairman.
In fairness to Vince, you can kind of see why he's reluctant to pull the trigger on Roman's long-awaited character shift. There have been several instances in the company's past where they've changed the alignment of a wrestler one week, only to go cold on the idea after a negative crowd response a short while later.