Don't forget that the industrial revolution only happened in the 1700s (which is 400 years ago). The medieval period (closest to classic fantasy) was in about 1400 or so which is 600 years ago. And that's only in Europe and North America. Homo Sapiens has been on the planet for about what? Half a million years? For most of that time technological advances in the way that we see them today were minute. So I guess you could say that taken in the round, fantasy societies are actually quite advanced!