I think the only way your key-signing mechanism would actually solve the problem is if we made it actively hard for new developers to upload projects to PyPI without a long vetting process. Some projects work this way (Debian, notably; I've had upload rights for a few Debian packages for years and still don't feel ready to apply for full access), but I think it's a poor match for PyPI's actual goal.
You know who does this sort of thing? Politicians. They can't just look at a working system, single payer for instance, and copy it. No, they have to make silly arguments about why it will never work, despite a concrete, working example, right in front of their own eyes.
If Python introduced manual review of new packages, it would either need a massive amount of resources that no-one is offering to provide, or it would immediately be a huge bottleneck on people making new packages, which the community doesn't want to do.
Lipstick on the pig, still covered in mud.
The key difference is the regular occurrence of malware finding its way into PyPi and NPM due to the lack of multilayered security on those repos.
You guys keep trying to prop up the straw man that ONLY package signing is needed. It's not. It's a start. Nobody is making that argument but you. You not only repeatedly beat that dead horse, but you carry it to the illogical extreme that package signing is somehow harmful. Not only do you see no value in that layer of security, but you actively resist any talk or attempts at implementing it.
Meanwhile, your repo is infested with hackers and malware. Big surprise.
My rough guess is that for the Python community, these are roughly proportional; there are a lot of different people maintaining approximately one library each, not a small number of people (or companies) maintaining large parts of the ecosystem. There's nothing directly like org.apache for Python.