If that was the problem then the UCs could just cut down their international student admissions to compensate. No, the problem is that the UC system as an organization is fundamentally broken, corrupt to the bone, and has all but lost sight of their intended purpose of creating and proliferating knowledge.
This is a strong claim, without any evidence to back it up. There may be some truth here, but against most metrics, UCs are among the top research institutions in the world with amazing contributions to science, medicine, etc. etc.
I thought the poster was quite clear. If the UC system can't support the top 9% of their high school population in-state, and exacerbate the problem with overadmissions, then it seems clear there is a systemic failure somewhere that someone doesn't want to admit.
