There was a time when some stuff was being extracted (removed) from Ruby core and becoming gems and I really tought PStore and YAML::Store were going to be among those, but no, they decided to keep them in core. So maybe there are some important enough use cases that justify it being there.

Or maybe it would be a hard task that didn't justify the effort.

Many parts of the stdlib are being slowly gemified, that's the case of `pstore` too hence why it has it's own repo.

It's now no longer technically stdlib, but a "default gem", a gem that is installed by default with ruby, see: https://stdgems.org/

Since a few years every version remove one or two rarely used default gems. The Ruby core team just doesn't like big breaking changes.