While it has been stated in this website before, I believe that it is worth repeating.
I think & believe that it is a combination of various issues (in no particular order of importance):
(a) Capital exchanging hands with the athlete, family, etc. (e.g. Ca$h, Gifts, promises to relatives, etc.);
(b) Families are in fact "pimping" their sons for the money and financial gains;
(c) Team results (e.g. winning record, appearance in national Televised games, appearance in Major Bowl games, etc.);
(d) Team's winning tradition, especially over the last 10-20 years (most especially over the last 5 years);
(e) Team's Wining Record on a consistent basis, year after year (with at least 10-12 wins per year mixed with some undefeated seasons, and some National Championships);
(f) Ability of the Team to place athletes in the NFL in a consistent basis (in particular the top 3 rounds of each draft, and most especially in the top 15 spots of the 1st Round, etc.);
(g) Quality of top level and highly recognized (and highly sought after) Coaches;
(h) Top coaches that can assess, recruit, develop, and motivate their star performers to bring out their "A+" game on a consistent basis;
(i) Historical Record of a Team that is consistently restocking, and not rebuilding;
(j) Local players are no longer longing/desiring to play for the home team (i.e. The U), and in fact want to see the world (i.e. go out of state);
(k) Etc., etc.
To overcome some or most of these obstacles, the coaching staff needs to develop and implement a highly thought-out & focused strategy (combined with specific tactics depending on the particular case).