The weirdest thing to me is that the Chinese had sky lanterns 2,300 years ago but they never scaled them up to hot air balloons. It took 2,000 years before Joseph-Michel Montgolfier saw some laundry billow as it dried above a fire, inspiring him to build a flying machine.

What amazes me is we've had hot air balloons for 250 years and still haven't scaled them into partial vacuum space zeppelins, we're still burning rocket fuel like it's the dark ages

I’d guess the answer is similar - there was no constraint on a key resource to act as a forcing function.