I think on one hand, the term Tuner is a stereotype of stickers, questionable body mods and ugly wings of the late 90's. Additionally, just like real car shows, there are the "old guys" who hate "foreign jap-BLAH_BLAH_BLAH_BLAH", or anything foreign.
I think they could just do an Import Class, because there is a huge variety of European, American, and Japanese cars that don't adhere to the Tuner style anyway.