Because HS HCs want to win and don’t care about developing QBs. Kinda like NCAA these days. Even the NFL seems to be adapting (kinda). Dual threat, ie RBs playing QB.
It didn't used to be like that. Terry Bradshaw, Bert Jones, Joe Ferguson, David Woodley, Stan Humphreys, Doug Williams, Mike Miley, and even the Booty boys were all good LA produced QB's. Probably a few more I have forgotten about. Allen Risher was pretty good. Also Tommy Hodson.s