That's fine, but gpg signatures would do nothing to prevent this and widy scaled webs of trust don't exist.
- macOS apps need to be signed (to run without extra work). The keypair is associated with a developer ID account that has a credit card on file. Abuse is still possible (stolen credit card, stolen certificate), but a lot harder.
- Some open source project have their own WoT. For example, IIRC NetBSD required new developers to meet with one or two existing developers in person to verify their identity. (Pretty much like a regular PGP WoT.)
These are more work, but they also make the world safer for users.
Debian also requires OpenPGP keys and WoT for all developers.
A web of trust implies transitive trust.
I'm pretty sure the same is true of Debian, but I don't know about the others. But these are NOT webs of trust.
What's more, other open source projects simply do not deal with the scale of NPM. The amount of data they move and offer is pretty brutal. Lots of dismissive engineers sneer at the javascript numeric tower and simply do not understand how difficult and perhaps even surprising the implementation of NPM as a platform is, given its scale.
Most people won't be that strict in informal development, but that's not really what this is about.