Could Asian immigration be playing a part in that? 2nd- and 3rd-generation Asians in America typically have grown up bigger than folks in their ancestral countries, but still tend to be smaller than black and/or white American natives. Increasing veganism could work to reverse that growth pattern.
Though I don't think that's anything Cowherd wanted to get into on his radio show, I absolutely think the West Coast's demographics play into not just (somewhat) waning player development, but fan interest and filling stadiums as well.
Asians males generally don't play high school football, much less college football, even if they grow up watching it. And though Hispanic males are active in high school football across the west, you don't see their numbers translate into college football as much as African Americans, of which both demographics have similar population size in the US.
However, Hispanic males do fill football stadiums and provide a huge TV audience for football, albeit mostly NFL. Working on a number of industrial job sites across Arizona and California, even the older Hispanic men who barely speak English have an NFL team. I've seen so many Cowboys, 49ers, Raiders, and Broncos stickers on hard hats of Hispanic construction workers. They just don't pay the same attention to college football.
To extend this to college football, let's compare UCLA to Michigan State or Auburn. Both the latter actively cultivate their students into lifelong fans and season ticket holders through a number of ways. It's a family thing, a campus wide thing, a local media thing, a statewide talking point.
At UCLA there's almost no undergrad interest in going to the football games. The population is not just Asian (American) heavy, but it's also boasts large foreign Asian numbers that've never come across football until a few days after landing at LAX. UCLA casts a global admissions net resulting in the type of highly competitive undergrad, even within the US, that doesn't see the college experience as also rooting for the campus teams.
Michigan has figured out to have it both ways. They net a plenty of foreign students and academically uphold a global reputation, yet Wolverines football is from what I can tell the single most followed team in the state of Michigan, whether college or pro, and fill their stadium.