Well, technological development did more or less. The Human Village lives much like it did back in the later 19th century when the Great Hakurei Barrier was constructed. Additionally, Gensokyo lacks any form of advanced electrical or gas-power infrastructure.
There is a belief that the highly electrical culture of our current society is detrimental for the formation/existence of various Japanese spirits, tsukumogami being one example, as well. Perhaps more common youkai demonstrate a lessened affliction from this.