The thing is Mandy have Kory's full name as her last name comes off as awkward, especially when evidence points to the -and'r suffice functioning as a last name in Tamaranean culture. In adapting it to an earth stylization, Anders is pre-established, or if Kory wants a more accurate to the original Tamaranean pronunciation, And'r would work too and make more sense than her full name.
I also doubt Tamaki has any specific reasoning or intent with making Koriand'r function as a last name. More likely she wasn't aware of the established naming conventions for Tamaraneans or the out-of-current-use Anders name, and didn't bother to do the research (which really isn't that hard to do. I got my research on this in five minutes from checking Starfire's DC wikia page)