Because most kids don’t look at colleges in the “bang for their buck” way. They look at rankings and prestige. It’s hard for the Cal States to compete – reputation-wise – with the UCs as a whole, considering how many Nobel Prizes the system has and how many of the UCs conduct world-class research. Also, quite a few of the Cal States are commuter schools, or have that vibe. It’s up to the parents to teach kids about things such as class size, access to faculty, and the worth of a particular degree (i.e., bang for your buck.)