It is a fair question and puzzling (outside of blatant cheating to get elite bigs to some schools).
1. Cal is almost a slam dunk to get elite bigs to go high in the draft by developing them, putting a system around them to showcase what NBA bigs need to do, etc... Outside of Skal I can hardly find a big that underplayed his skill before UK to what he ended up playing in college. Cuz, Nerlens, AD, KAT and now Nick are bigtime bigs in college. Heck even Jorts had a cup of coffee in NBA which was unheard of. Dakari is a guy who simply had KAT over recruit him and then Dakari left too soon.
2. Isn't Cal a better bet at bigs vs. his pedigree which is PG? And I think Cal is a magician with PG prospects but I think he's even a bit better with the bigs.
Why guys like Bamba, Zimmerman, Isiah Stewart, etc...go to schools like Washington, Texas, UNLV, etc.. are just risking it for very little sense. We'll see if Penny Hardaway can churn out good bigs as looks like he's the next guy to pull guys away from UK to Memphis.