In a lot of countries, especially Japan, bathing in particular is a big thing, hence the prevalence of bathhouses. The fact that they clean up before they get in the bath means it's just as clean as showing. The soaking is honestly just relaxing. I myself go out of my way to have a bath at least twice a week and shower for the rest of it.
Also the water bill there is cheaper than in the US.
where I'm from, baths are extremely necessary and those from poorer families or who're renting places without bath tubs, fo to a bath house. Few people take baths in the summer though but from fall to spring it's bath bath bath all the time
I don't know why there're so many manga with characters obsessed with bath. From my experience, people almost never ever take bath. It wastes a lot of water and takes a lot of time. Plus, showering is cleaner than taking a bath.