> The commit history should be the primary source of truth for what changes have happened.

It's just super impractical. The work is discussed / documented in the project management systems, I'm not going to copy it extra (from design document, the ticket description, ticket discussion, screenshots) for the SCM. Too much work, too small benefit.

> I've also been at orgs where they've switched from one ticket tracking software to another, and haven't maintained history, or even when they do, the ticket ids and up changing afterward.

I've been in orgs where they've switched SCM and didn't keep history. Neither should happen.