Usually, they are missing major requirements, although as above poster said, if it’s truly a highly selective major, they might take ECs under consideration.
Another thing never mentioned- suspected plagiarism. A poster up here a while back, 4.0, all req completed, tons of related ECs. Applied to Communications. Rejected at UCLA. Well, ok, it’s a tough one, but a bit surprising; then rejected at UCSD. This seemed doubly odd. He did get into UCSB so I knew it wasn’t a unit issue. My first thought was they don’t believe he wrote his essay (or something similar). I have no idea, but it entered my head.
The mom of a friend of mine reads scholarship essays for SCU and she says sometimes it’s glaring that someone else wrote the essay.
He also could have been lying about his 4.0.