What if you're on Windows where it's much less convenient? Also, latex and others substitute that for the proper dash, so one might do it out of habit.

Also also,it's en-dash, not n-dash. And it's correct in British English, where the em-dash largely fell out of use.

Ok. Today I learned. But I'll still continue to use -- because I don't care enough to be correct and most people will understand me regardless. Being pedantic about it doesn't seem very productive.