Everyone will mention uv/pyenv/poetry/conda/virtualenvs, so fine, let's pretend it's not a problem that you tried each of those in desperation and they are all household names. Suppose the packaging wars actually ended and everyone uses what you use without you needing to tell them, and suppose further that every pypa problem isn't blaming debian maintainers for obvious regressions. Pypi will still yank[0] packages at the source to perhaps randomly break deterministic behaviour, smashing anything in the blast radius rather than only clients using a --strict flag or something. You can pin your own dependencies but who knows what they will pin (nothing, or the wrong stuff, or the wrong way probably!) or what they will yank. Now for repeatability you need to host a mirror for everything you use- which is fine for corporate but a nonstarter for the novice and annoying for FOSS projects.
If you have zero dependencies or a slowly changing environment that is receiving constant care and feeding, you'll probably never notice how bad things are. If you put down most projects for a month though and pick them back up, perhaps with a different environment, machine, or slightly different python version it's broken, bitrotted, and needs serious attention to be rehabilitated.
People might argue.. that's just software dev. Nope. I say it with lots of love and gratitude for the efforts of the community.. but most langs/ecosystems would never tolerate this level of instability. One has to eventually just admit that working, portable, and actually repeatable environments with python basically just require docker. Can we talk about how "--break-system-packages" is hilarious? After you retreat to docker you can type this a few times a day, push the container up, pull it down months/years later, and then realize that literally the only way to get a stable working environment is to request a broken one. QED