Bathing practices vary sharply between countries in ways that surprise travellers. Most of the variation traces to one structural question about where the washing happens.
Washing before entering changes everything
In traditions where a person soaks in shared or reused water, washing must be completed before entry. The bath is for immersion rather than for cleaning.
That single rule requires a washing area outside the tub, a floor drain, and a room designed to be wet throughout rather than only inside a basin.
Where washing happens in the tub, the water is used once and drained, so the room can be dry outside a single enclosure and no floor drain is needed.
The plumbing follows the custom, then enforces it
Buildings are constructed around the prevailing practice. A wet room with a central drain and a deep tub is a different construction from a shower over a bath.
Once built, the room constrains what its occupants can do, so the custom is reproduced by the housing stock long after any original reason has faded.
This is why the practice persists so strongly across generations and why it changes mainly when people move into buildings designed for a different pattern.
Communal bathing depends on the same rule
Shared bathing is only workable where bodies are cleaned before entering the water, which is why public bath traditions cluster in exactly those cultures.
The etiquette in such places is detailed and strictly observed, covering where to wash, how to sit, what to do with a towel and how to enter.
Visitors frequently read these rules as formality. They are the operating requirements of a shared water system, and the tradition does not function without them.
Heat sources shaped regional forms
Where geothermal water is available, bathing developed around naturally hot sources, and the buildings were sited by the spring rather than the other way round.
Where fuel had to be carried and burned, heating water was expensive, which favoured practices that used less of it or shared a single heating.
Steam-based traditions arose partly for the same reason, since heating air and a small quantity of water consumes far less fuel than filling a tub.
What the bath is for varies as much as how
In some traditions bathing is primarily cleaning, performed quickly and privately, and speed is regarded as sensible rather than perfunctory.
In others it is a period of rest with a social component, where the time spent is the point and hurrying misses it entirely.
Neither reading is a preference about hygiene. They are different activities that happen to use the same water, which is why each looks strange from inside the other.