Here is Alabama coach Nick Saban demonstrating that he doesn't understand marginal analysis.
This is a very self-serving statement he makes, and his players are showing that they're better at choosing for themselves than he is at choosing for them.
After dozens of games played, one more game isn't going to rocket them up the draft chart, while they risk career-destroying injury.
And if NFL scouts take the combine seriously, then so should the players, even if, as Saban says, a lot of what they do there isn't relevant to real football.
And that's a general truth in political economy - people are better at making decisions for themselves than for others.