To be honest, they shouldn't do so directly. For the obvious reason you stated, they don't have a SLA to you or your company. But also because it is a shitty thing to do as a company. Companies should have their own proxies and mirrors for any repository they pull from. Both to be in control of the dependencies you as a company rely on and to not unnecessarily put load on free third party repositories.
Had not heard of your solution. More often than not I come across Harbor, Nexus or things like GCPs internal stuff.
Maybe I'm out of touch, but I think control over dependencies is underrated. It's not just about freezing and pinning. There should be better tooling to support the whole dependency evolution pipeline. For example updates should be reviewed/ingested/integrated/validated based on local policy not based on source release schedule.
The problem is, there's a difference between doing that for a handful of C or Go libraries, versus trying to vendor thousands of NPM libraries and all of their interdependencies. So it's very ecosystem dependent.