Let me put it this way...
Switch, by definition and in other sports, is used to described something as UNNATURAL.  The reason people call or describe things as switch or unnatural, is because when you watch the trick, you don't know whether it's that person's natural or unnatural version.  One person's natural is another person's unnatural.  You need to call it "switch" so that people know you're doing it unnatural.  "Switch" is a distinguishing word used when, at first glance, you don't know whether a trick is natural or unnatural.
With skiing, it's pretty damn OBVIOUS that skiing backwards is not something that is natural.  It never has been and never will be.  Therefore, calling backwards skiing "switch" is a bastardizing of the true meaning of the word "switch".  That is why there exists the term "FAKIE", which is what people should have used from the beginning, but for certain pro skiers back in the 90's thinking "switch" sounded cooler -- bad reason if you ask me, because now everyone in skateboarding, in-line, snowboarding, etc. think we're looney.