Speaking as a mut from the south, specifically Texas,
I will give you my take. Texas, as a state, produces more
Div I scholarship athletes in football than any other state
for two major reasons:

1. Texas is the 2nd most populous state. (thank you peegarden the obvious)
2. Texas emphasizes football like no other state
on the High School level. It is a huge cultural thing.
The High Schools revolve around football teams.
The bands, the numerous dance teams, the ROTC
I can keep going... are huge organizations that football
spawned. Friday nights (Its now really Thursday, Friday, and Saturday nights) are huge events. All these little Texas towns cultural activity is centered around football. It is quite extraordinary.

Climate is not the whole story. Many parts of Texas are excessively hot in the summer and in the panhandle, cold in the winter being along way from the Gulf warmth. California has a much more moderate climate overall and since the majority of the population is next to the Pacific (which moderates temperatures in summer and winter) they should have all the players. But California does not on the High School level. So the climate factor is not as important as the cultural one.

Texas is football crazed. Heck, the Big 12 is really conference Texas. Every team in the Big 12 this year had very good players from Texas. LSU recruits heavily in East Texas, Oklahoma has about 50% players from Texas and usually their very best players from North Texas. Nebraska use to rape Texas of players, but they dont anymore and look what happened.

Jeez Louise, even Miami, Florida, and Florida St. get great players out of Texas. One of the best RBs in the State is going to Michigan. 2 of the top lineman going to Notre Dame... on and on.