For the same reason it’s called “Azure Database for PostgreSQL”, whereas the sensible name would have been “PostgreSQL Database for Azure”.
If Microsoft is putting someone else’s trademark (in this case Linux or PostgreSQL) in its product name, their own trademark will always come first and someone else’s trademark will come last.
If Microsoft is putting someone else’s trademark (in this case Linux or PostgreSQL) in its product name, their own trademark will always come first and someone else’s trademark will come last.