Why are hot springs such a big thing in Japan? Third attempt

Looks like it might at least partly have got popular simply because it was allowed when so many things weren’t:

“Although the [Tokugawa] shogunate prohibited travel in the interests of preserving order, it allowed pilgrimages, visits to relatives, and trips to medicinal hot springs

 East Asia A Cultural, Social and Political History pg 345

Why do Japanese slippers only come in one size?

This is one of the oldest gaijin complaints about ryokan (Japanese-style inns) etc, but if you look around you’ll notice that plenty of Japanese are hanging out of the back of their slippers too, and different sizes of yukata are usually available to match the size of the rest of your body, so it is not that there is a lack of awareness that people come in different sizes.

You don’t have to wear them for too long, what with them coming off or being exchanged on tatami, in the toilet or outside, and it’s no problem walking in any size of them if you shuffle properly. More important, I believe, is that – like a tiny towel held somewhere in the vicinity of your genitles in a hot spring – slippers are more symbolic of cleanliness and taking care than they are practical. This can also be seen in the fact that slippers are often exchanged for shoes in an area that both touch.