1) Everyone thinks they can make it at the next level, but how many actually can? (answer: very few) You'd get a lot of guys delaying missions and probably not going off the shadow of a hope that they won't ever make, and possibly not going on missions because of the inconvenience it causes in their lives (it is easier to go fresh out of HS when you don't have anything better to do than after college when there's money to be made and bills to be paid).

2) BYU has built its recruiting pipe around the current system. There were hiccups when they switched mission ages, but it wasn't that big of a deal because the basic model stayed the same (IIRC, Mika was asked to not go on a mission so he could contribute last year to help bridge the transition of the BB team while the rest of the Alpine kids went out of HS; I wouldn't be surprised if athletes from other sports were asked to do the same). However, if you start encouraging sports first mission after, you're going to load teams with young talent, as guys come off missions they only add to young talent. You'd get an overload of young, inexperienced talent which would lead to two things: young, inexperienced teams; and having to send guys away b/c there aren't enough schollies.

I guess 3) if you emphasize sports first, mission second (if at all) you're making a comment (intentionally or not) about where priorities should be.