I've been mulling over this for the better part of the day as the heat in SEA makes everything worse.
Aside from the more obvious effects the Outside World has on Gensokyo (like the fact that Gensokyo is basically a garbage dump for forgotten things and presumably, people), is it also affected by less obvious aspects, like weather changes, climate change, pollution, earthquakes and the like?
Is the Great Hakurei Barrier that imposing on the unchanging state of Gensokyo that it simply blocks ANY change the Outside world might cause on it? Or are the inhabitants entirely to blame for its eternal state?
I like the worldbuilding touhou has, but this constant push against change is somehwhat worrying (at least for the hapless humans that cant ever progress socially and technologically due to their unfortunate position as youkai or god food). It is an interesting premise, but i am still saddened by the this unchanging state it is in.