I don't dispute that a mobile QB in the NFL will open up a few more doors if you don't have a good scheme and players in place. Those runners tend to be much better athletes, and can occasionally make something out of nothing.
However, that method is only going to buy you short term gain. Your QB is going to end up spending more time in the infirmary if he keeps running. Those 190 lb safeties that he ran over in college are now 215 lb freaks of nature, and all of them are fast and strong. Those 220 lb linebackers that he would take head on and come out ahead most of the time are now 250 lb monsters that hit with frightening power and speed. The "weakside" defensive ends who were 240 lbs could be either outrun, or even taken on once in a while are now 270 lb bruisers that can now run down any quarterback.
In the pros, everyone's fast, strong, and big (for the most part), and even a 250 lb freakishly good athlete the likes of Cam Newton wasn't able to handle more than a handful of years of getting pounded while running.
If I were a team owner, I wouldn't be looking at running QB's, especially if they are to be the face of the franchise. They're just a few hits away from having their vast potential becoming castrated. That, plus you wouldn't run that big of a risk of wasting salary cap space.