Except pip still exists and is default, and even if they adopted uv as default instead, all the legacy stuff takes years to change.
Who are "they"? I am not waiting for anyone to adopt uv. I've adopted it myself and forgotten about pip as uv is pip-compatible for all practical purposes.
Compare to npm which has been the default installer/manager in NodeJS since forever, so it's totally supported, and any git repo you happen to download has a package.json