Considering Deposit at Two Universities Due to the Unknown - Anyone Else?

What they actually did was strictly enforce the stated conditions of admission (submit final high school transcript by a certain date, with a sufficiently high senior year GPA and no D/F grades), rather than the probable leniency given in other years.

https://www.latimes.com/local/lanow/la-me-uc-irvine-rescissions-20170728-story.html says that 499 were rescinded in 2017, 290 for transcript issues (probably missing or late final high school transcripts) and the rest (209) for senior year grades or GPA being too low.

In other years, they may have let slide a slightly late final high school transcript, or a 2.9 senior year GPA. But the conditions of admission did not guarantee such leniency. Just because a clearly stated rule was not enforced the last time does not mean that it will not be enforced the next time.