Except Assimilation is not what a Liberal is looking for. They are, quite on purpose, dividing people and putting them into groups (well the politicians and leaders anyway, not your average brain dead Liberal). When you have people in groups you can pit one against another, you can build group politics and thereby being able to appeal to a single issue and stroke a single ego, and decry any change as "racist).
Hence the -American isn't a means to be PC bur rather is means to
A. seperate them as unique individuals, who are not American but their own "kind"
B. Give them they own identies and be able to refer to group not an individual for any policies/grievances.
C. Imply that any personal problem you had wasn't a result of your own...