Why is NPM still so buggy and slow?

So NPM is on version 9 or so, and it is still as buggy as ever. All kinds of weird errors, which I don't get when I use yarn or pnpm. It's also comparatively slow.

Why exactly is NPM still buggy and slow after all these years? What are they doing wrong?

For some reason I'd really like to stick with NPM, but the fact that its competitors manage to be consistently better means I might have to bite the bullet and make a permanent switch.