Why aren't MacBook alert sounds synced with iPhone's?

(MacBook Air, mid 2013 / Big Sur 11.1)

My MacBook's alert settings are different than my iPhone's...why is that? I'm properly signed into iCloud and everything syncs perfectly but my alert sound preferences.

For example, when I open Contacts on my MacBook, I can see alert sound preferences I have made for specific contacts (eg., family members have an alert sound that isn't the default). When I'm on my iPhone and receive a iMessage/text from a particular person it plays the chosen sound, not the default.

But my MacBook doesn't reflect this and instead plays the default iMessage alert sound for ALL incoming messages, despite Contacts on both devices showing specific changes. It's been this way for 7 years. Am I missing something?

Thanks in advance!