For example, the vast majority of the code I write is AGPL-licensed (derived from an AGPL licensed work by a third-party), yet you won't find a copy of it on the Internet. That's because we only have to provide that source to our customers, and while it's fully within their rights, they have no inclination to share it with anyone.
Sadly, I doubt the FSF will ever write such a license, given how they discourage use of even the LGPL unless absolutely necessary.
Setting up a web service with GPL code doesn't meet the bar for distribution, so that situation does not require the code to be made available. That's what the AGPL addresses, network use triggers the requirement to make the code available.
The obvious case where that wouldn't work is a project like Linux with many contributors and no copyright assignment. But others like Clojure organize themselves differently.