I just don't understand how this can happen. In Maven Central for example (Java) if you publish a package it is immutable and stays there until nuclear fire immolates the Earth.
Unless I'm misunderstanding something about Central's architecture, it's not fundamentally different from NPM in this regard, though signing appears a bit more feasible.
Which means that it's not a technical difference. Maybe Central has been compromised/had issues before, just long ago (it's certainly much older). Maybe there are things wrong with NPM-as-a-company even if NPM-as-a-technology is fine. Maybe it's just luck.
But "stays there until nuclear fire immolates the Earth" sounds a bit much like "this ship is completely unsinkable" for my liking.