PyPI's architecture isn't meaningfully different than npm's. Npm has seen more high profile incidents because:

1. Packages tend to be smaller, and the transitive dependency trees of projects corresponding larger. This means there are more single points of failure.

2. More people are using it.

Python, and for that matter most language package ecosystems, have the same problems as js, but many of them have gotten away with it for a bit longer due to (lack of) scale.