Does the local backup with iTunes not include iMessage?

I don't know too may users who care only about a specific aspect of their phone when backing up. I do have non-technical friends who do iTunes/local backups because they "don't trust the cloud", but I've never encountered a person trying to do this piecemeal.

For what it's worth, there are decent 3rd party tools like iMazing that are easy to use and do give you more granular control.