Here’s the classroom inventory at UCLA:
https://www.registrar.ucla.edu/Faculty-Staff/Classrooms-and-Scheduling/General-Assignment-Classroom-Inventory
And here’s another list of the classrooms with seating charts and pictures:
https://www.teaching.ucla.edu/avs/classroom-list
The largest class at UCLA is still Moore 100, and it’s listed as having 420 seats. When I attended, it was closer to 500, so they must have done something to it by remodeling. Seating probably wouldn’t matter now that most of the classes are Zoomed, so it appears that classes are less capped. I’d expect a run on enrollment for at least fall term, in classes that would be perhaps harder (at least perceptively) when in-person.
The lower division chem classes would be extremely popular with all the premeds, etc., at UCLA – per ucbalumnus’s point about popular majors and classes having larger enrollments, so it isn’t a question of Ivies and medium-size elite colleges not having large LD classes either. There are various social-media types who video their finding seats in class at whatever Ivy, and some of them look to be at least a good 250-300 students.
There’s an article about Stanford’s average CS class being ~ 120 students with a larger student-faculty ratio, because I’d imagine that CS professors would be the hardest to find, so again there’s the popular-major theory that is manifested with respect to its enrollment. I’m guessing that CS classes all across the country are large, no matter whether public flagship or small private. (At least relatively speaking – e.g., for a Caltech student, the perception of a large class might be ~75, not 400.)
And any notion that UCD’s classes are smaller than UCB’s and UCLA’s would be erroneous.
Edit: And let me add that students and their parents across the nation already know that UCLA and UCB have large enrollments. That doesn’t stop a school like ASU and other public universities with larger enrollments from being less desirable, but undoubtedly for various reasons.