Because different use cases have different requirements. So having the maintenance command be separate from the filesystem gives ultimate flexibility.

The OP comment didn't give any context for what you should be thinking to make a judgement call on. Just blindly "run this command periodically". If I'm not making any actual decision, it should just be run for me by default.

Does your car wash itself? /s

It very well may be! Depending on your distribution... they may already have similar services/timers for periodic scrubbing

On Fedora they aren't provided; but are with Arch

Unless you run an array it's fairly meaningless, beyond being an administrative-reporting tool. It can't fix failed checksums without mirrors or parity

I think the checksums are validated on read anyway, so it's mostly to mitigate bitrot - very specific to 'glacial' storage

> If it was a good idea, I assume it should already be happening for me.

It would, if you were running a well-designed/maintained operating system. Unfortunately many Linux distributions make poor decisions.