Some coaches don't necessarily need the kind of talent that you would have to have in the NFL to be successful. Oregon has a lot of players with speed that wouldn't really be all-around great players in the NFL. That's the system that Kelly runs, and those are the kind of players that they need. Same thing goes for some of Urban Meyer's offensive players the past few years.
Guys like Tebow have proven over time that you can truly shine in CFB without transitioning that talent to the NFL.
Some guys are 10/10 in any one category. WRs in college can get by being REALLY good at 2 or 3 of these things only:
-they run great routes
-they have amazing hands
-they can JUMP
-they're strong/physical
-they're incredibly fast
-they can block for the run game
-they're a leader
-they can stay healthy
-they're incredibly smart
of course this is also contingent on them not being morons off the field
in the NFL they'd have to be great at 5 or 6 of those things, and 8/10 on the rest.
The fact is that there's only 32 teams in the league, and there are 124 FBS teams. Not to mention that talent is also pulled from teams outside of the FBS for the NFL.
In college you find talent where you can and you plug it into your system. Some teams have the pick of the litter, some have to make it work for themselves.
The coaches who can handle that discrepancy the best are respected (Boise), the coaches that earn their way and get the best of the best are envied (Bama), and the guys who can't do that get canned (UK).
Also, guys in CFB with talent can shine early and throughout their career. A talented DL can come in and prove their worth early working against upper classmen, then spend their last 2 years destroying guys that have only been starting on their OL for 1-2 years.
Once they jump to the NFL, they might line up against someone who has been starting on their pro team's OL for 6 or more years. It's hard to continue that dominance when you're facing someone who can handle you.