The UC’s are paid for by the California taxpayers.
Aid goes to the children of those taxpayers.
The UC’s admit OOS and international students because those students pay full fees. If you are trying to get a “merit” scholarship at UCSD, at best, you would get maybe $2500 per year. Where would you get the rest of the $52500 per year?
Outside scholarships won’t cover that because the best financial aid comes from the colleges themselves.