What interests me is why humans crave this one time in history (medieval?). It’s old enough to be different than now but not old enough to be like caveman times? Lower technology than now but not no technology. Do people in other countries that aren’t western civilization have similar cravings for that era or an era like it?
I would guess that a large part of it is that it's the oldest period of time for which we have significant details, and a strong association with the people there as our ancestors (in the respective countries where such fairs are prevalent). We have much less idea of what ancient Roman or Celtic or Norse or Thracian etc day to day life actually looked like, and to the extent that we do know, it's much weirder and more foreign.