Given RmP is largely regarded in the field as easy to manipulate garbage that shouldn't be used in evaluation and is profoundly biased in it's ratings, I don't think I'd be happy for my product to be called "RmP for X".
Rate my professor isn’t for people “in the field” though? The primary audience is students, not other teachers. That’s kinda like saying folks in the movie industry think Rotten Tomatoes is garbage. Who cares what they think?
Probably for the same reason that if my restaurant rating site kept spitting up "Taco Bell" as the best mexican restaurant in town, I probably wouldn't be pleased.