Congrats on CS admits at UCSC and UCSD.
I agree if students commit somewhere, they should decline their other admits, it’s the right (and easy) thing to do.
But…this won’t necessarily turn waitlist slots into offers. UCLA likely planned for a Class of 2025 yield of around 40%, so they already have accounted for 60% of admitted students turning down their offer of admission. UCSC baked in a yield of around 12%, and so on.
With that said, it is likely these schools will be going to their waitlists, we just don’t know what they each will be needing after they account for gender, major, OOS vs in-state, etc.