I don't think it's the problem.

I think that it's a combination of two things:

1. many webdevs just have no clue what a thread is, because generally, they don't need it, so it isn't taught;

2. most of the documentation you can find online was written by people (and now ChatGPT) who don't understand async, sprinkle the word randomly and tweak things until they seem to work.

As a consequence, webdevs learn that async is magic. Which is a shame, because the underlying model is almost simple (the fact that we have both micro-tasks and tasks complicates things a bit).