Keep in mind that prior to 1986, applicants could only apply to one UC campus, so applicants were very careful to use their one best shot at a campus that best matched their stats. A couple of people mention it here. http://talk.qa.collegeconfidential.com/discussion/comment/21526591/#Comment_21526591
Students who were rejected but otherwise met the UC minimum eligibility requirements had their apps redirected to another campus with available space. As a result, there was a huge disincentive to apply to a reach campus unless they were OK with going to Riverside, as that might be the only campus left with available space by the time their apps was forwarded on from their top choice.
Once the “one campus” policy changed in 1986 to where students could apply to multiple campuses, the number of apps increased drastically and the acceptance rates went from the mid 50s to the mid 30s for Berkeley, and the low 70s to the low 40s for UCLA. High by today’s standards, but about what you might expect from that era.
Here’s an article from 1988 that talks about how many students with 4.0s were being rejected from Berkeley and UCLA even then despite those higher acceptance rates. https://www.latimes.com/archives/la-xpm-1988-02-12-mn-28540-story.html