PRs are all about power dynamics and (un)spoken deals…

If you rubberstamp some people‘s PRs all the time, you can then get them to greenlight your unpleasant PRs via pm instantly.

The other way round, retaliation: I once added some serious review notes to the PR of a very senior engineer because it was a dangerous topic. He would then spend the next months nitpicking every single PR I created. Had to post my PR in slack whenever he was not online to get them merged. After that I never seriously reviewed his PRs again. Too much of a headache.