1. At least 99.99% of NFL players for the past 50 years have played at least some college football. So you are correct in that regard.
2. As to why the games are vastly different, it's a matter of numbers. Colleges are allowed to have 85 scholarship players, and most usually have another 10 or so not on scholarship. There's 119 Division 1 teams, and probably another 400 or so lower division college teams (which do usually have smaller rosters; call it 60-70). There's 32 pro teams, all of whom are limited to 53 players on the roster. Also, although the average NFL player's career is only about 3 years, there are quite a few who last a lot longer, whereas colleges turn over essentially their entire roster every four years. Maybe 2% of college football players ever make a pro football roster, and most of those don't hang around very long. So, the players who do play pro football are absolutely elite athletes; they are much bigger, faster, and stronger than college football players. Thus, a lot of the stuff that works in college football when your team places an elite athlete in position against a non-elite athlete just won't work in the pros, where everyone is an elite athlete.
The other main reason that a lot of stuff done in colleges never makes it to pros is because pro coaches tend to be fairly similar personality types, and usually are about as conservative and traditional a lot as you will find. They're a risk-averse breed whose every tactical decision is ruthlessly second-guessed by the media and public at large. Therefore, if they're going to break with tradition, they'd better succeed. But it's easier for the coach to try the same strategies as everyone else and blame the players for their failure to execute if the team loses than it is to try something novel and absorb all of the assessed fault, or rather, it's less likely to get a coach fired.
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