How are you figuring those odds?
Let's say that there are 20 players from each school eligible to enter the draft each year (which is a pretty high estimate). There are 129 FBS schools, which would be a draftable pool of 2,580 players. If you want to even go more aggressive and say that some FCS, DII and DIII players get drafted every year, round it up to 3,000. That would make it about 8.4% odds.
Unless, of course, you're throwing all the draft-eligible players from across FCS, DII and DIII into the mix - which doesn't make sense, since almost all draftees every year come from FBS. In reality, for an FBS player, the odds of getting drafted are about 9-10%, for FCS probably about 1-2%, and for DII and DIII probably about .05%.