Google Maps is marked as dependent on the Google Services Framework, but it clearly doesn't use the same map tile rendering system that MicroG uses. I guess Google Play Services is only used for the logged-in features, which privacy-conscious users would avoid.
This could be the explanation. I never log in. :)
Irrespective of privacy, I am just not interested in the personalisation or, e.g., reading email on a phone.
I don't log in either, but Google Maps has an offline navigation feature that's restricted to logged in users:
https://support.google.com/maps/answer/6291838
Instead of using this, I have Here WeGo installed as a backup app for offline navigation:
On the phones I have tested Google Maps works with Google Play Services turned off.