“…probably looking for prestige or exclusivity. If that were not the case, they would not be excluding UCSC, UCR, UCM, and other CSUs from their application lists.”
Not necessarily. There are other reasons CA students don’t apply to some of these colleges: For example, Merced is in the middle of nowhere with a a crime rate 45% above the national average, has zero sports (other than club), no long-term track record of excellent academics; UC Riverside is located in well, Riverside, which is not a great area to go to college; has a commuter feel to it with many living off campus, and doesn’t have the same quality of students compared to the other UC’s you mentioned that are more popular.
Again, nothing wrong with these institutions but there are factors other than reputation/prestige why students choose not to attend them.