Contact Photos Missing in Messages App on Macs

This is a perennial question on these forums, and I've never seen it addressed satisfactorily.

I add photos to my frequent contacts in the Contacts app. I have two macs, one is a Mac Desktop, 24-inch, M1, 2021. The other is a MacBook Air, M1, 2020.

Here is a screenshot of the Messages app on my desktop.

And here is a screenshot of the Messages app on my MacBook:

Why? I am running the most recent version of Sequoia (15.7.2) on both machines. I realize it's not the most earth-shattering question, but why does this not work? I sync Contacts to iCloud, and the images show up there, too. What is going on here???