Why aren't these teams choosing something else then? If everyone on the team dislikes git, switch to mercurial or something else.

Because often it’s not the team that chooses, but tooling is instead standardized across the enterprise. And enterprises like to make the “safe” choice of choosing what’s most popular. And then there’s the whole aspect that you have to know some basic Git anyway to debug your way through the open source code you use (maybe not for JavaScript/NPM, I don’t know). Git also happens to currently be the most interoperable with other kinds of tooling, from CI to IDEs, so not using Git makes your life harder in ways unrelated to its inherent qualities. It’s a network effect in multiple dimensions.

How did it get so popular if disliked by the majority of dev?

Because generally people picking the tools are not majority of dev. They are architects or Senior Developers who do enjoy learning new things.

Also, git generally does just work and most IDE/Source Control Systems take care of basic operation of pull/branch/commit/push/open PR.

I suppose. It might seem a bit perverse after all if the non-engaged, uninterested in coding, clock puncher devs got to make all the decisions.

Popular as in “everyone is using it”, not necessarily “everyone is fond of it”. How did Jira become so popular? The dynamics that lead to such outcomes are interesting, but hardly unusual.

Git might be the best thing there is today (outside of very large companies or environments with large binaries). It doesn't mean that'll always be the case... There were other VCSs before git, and there will be after.