Yes, California is huge. We all get that. But the relevance of that fact in this context is dubious. California’s poverty rate (13.2%) is only slightly above the national average (12.6%). Some other high population states like New York (14.5%) and Texas (16.1%) have poverty rates significantly higher than California’s, with the consequence that although California’s population is nearly 50% larger than that of Texas, California has only about 30% more households living in poverty than Texas (4.7 million to 3.7 million). So there’s no shortage of low-income Texans for that state’s leading public universities, UT Austin and Texas A&M, to go out and find. Yet only 17% of each of those schools’ student bodies are Pell grant recipients, acording to NY Times data—more than most public and almost all private universities, to be sure, but nonetheless well below the figures achieved by at least 6 UC campuses. (I’m not sure why the Times excluded UC Riverside).
I think ultimately it’s a question of political will. California has always viewed upward social mobility for the least advantaged as one of public higher education’s most important functions. Consequently, a succession of legislatures and governors have generously funded need-based FA to an extent unmatched by any other state. A few other public flagships—Virginia, UNC Chapel Hill, and Michigan–meet full need (in Michigan’s case only for in-state students so far, but they’re in the midst of a $4 billion capital campaign that will raise sufficient funds to extend that policy to OOS students as well). But those are individual university policies, not state legislative priorities. A few other states provide fairly generous merit aid, but much of that goes to higher-income students and it doesn’t do as much to guarantee access for low-income students. And it’s also a question of political will and institutional priorities within the administration of the UC system, because it’s hard work to go out and find and recruit that many academically capable low-income students, yet they do it year after year. For other states and other universities, both public and private, upward social mobility has simply not been as important a political or institutional priority.