Last 11 seasons I have had, I believe, 8 first round draft picks from Zaga, 2 were drafted #1 overall. Prestige plays a role... but you have to be able to recruit first round draftable talent to have one taken in the first round.
Much bigger issue is the lack of Mid-Majors who are good enough to take top-20 type players away from the Big-6 schools than some unforseen logic keeping short guys from small schools on a "Black List".
to clairify what I am trying to say:
In the current game it is VERY hard for a mid major, (with limited funds and prestige), to recruit a 1st round draftable player. Most of those guys will be swept up by the bigger, more powerful, (and richer), programs. Therefore you won't see alot of 1st round picks coming from Missouri State, or UNLV, etc, unless a group of coaches come together... fill a mid-major conference.... raise their individual prestiges to the level (B+ to A+), where they can recruit a top-20 overall player. (this can take 10-15 seasons to do from scratch).
I can be done, and in some places... ie: ( Zaga in Allen, the C-USA in Rupp), players are actually being drafted in the 1st round pretty regularly.