I think there's a simpler explanation here.

pip solved a lot of baseline problems. It doesn't solve all of them. There were a bunch of failed attempts to be "better pip". They have not worked, really, but people stick around to some tools despite this.

I do think uv is different, on account of working and being very reactive to ecosystem pains.

(direnv is not Python-specific! It's just a tool to set env vars in a directory. But because Python venv's can work through setting two env vars....)