I'd imagine that, for a substantial percentage of these, part of it is to avoid negotiating and bargaining over an additional tool in your CI arsenal, especially in bigger corporate environments where these sort of conversations are dragged through layers of non-technical middle management.

The only major opinionated tools that were in use prior to uv were Conda, Pipenv and Poetry (- ignoring pip here, as it's mainly a package installer). None of them contributed towards PEP 518 (Conda significantly predated it, and Pipenv actively created a competing format even though the PEP already was accepted).

Most of the lessons that make uv good can be directly traced back to Cargo (which in turn can be traced back to Bundler). The main portions from the Python side that helped it have a good foundations were standards work (PEPs), none of which were driven by the people behind any of the three "major" package managers.

Poetry?

Yup, I ended up learning docker because Python packaging was such a dumpster fire.

I'll never forget the day I discovered that pip didn't do any dependency resolution. You had one job, and yet...