It's unexpected to anyone with intuition about how a computer traditionally is supposed to work. As a general principle, as a user, I expect a file on one computer to be usable on another computer. Or, at the very least, if I need to obtain some other thing from the original computer to "unlock" that file, I should be able to do it. The idea of a file that is only usable on a particular computer feels weird.

It's also unexpected when you send your laptop in for a screen replacement, the tech does an unnecessary logic board swap while he's at it, and your local keychain doesn't work anymore. And then Apple Support will say, hey, we told you you needed to backup your data! Which you did, but that's not the issue.

Use iCloud Keychain or don't use Keychain at all.

I've done Tahoe-to-Tahoe migration assistant moves between machines in recent months. No issues with login keychain migration.

Don't backup keys, rotate them.