Is there a term for the opposite of cargo culting? Where everyone avoids something, but no one remembers why? Because that’s basically where HTML tables have ended up.

I think this is something like a "delayed cargo culting", or "cargo culting based on outdated facts". I think it's basically the same as the hypothesis from the "Monkey Ladder Experiment", where monkeys got punished when trying to get a banana, and eventually all the monkeys were replaced with monkeys that didn't realize why the banana was off-limits, yet persisted in trying to "help" other monkeys trying to prevent them from getting the banana.

I'm not sure if I read that that specific experiment was debunked or not, but it certainly sounds familiar to how some developer trends get propagated even though the ground truth as changed.

I would guess that people became so afraid of being accused of using tables for layout that they don't use them at all.

It's still cargo culting