[wizofaus]

I can just imagine the reaction of a stone-ager being berated because they hadn't come up with "literally just a fatty acid salt with some phytochemicals that have antimicrobial properties". I suspect you could pick just about any tech invented in the last decade and describe it as "literally just a pick-your-adjective noun with some other random nouns that have something-or-another properties"...

Explain again why anyone would stop needing soap? (other than having departed this world...)

[frostwarrior]

Turns out soap is not THAT essential to personal hygiene, if you have running water.

The point of bathing is to rub off dead skin cells, excess oil off your skin (note that I said excess). And you can actually do all that without soap.

Also note that sweat it's not that stinky when it evaporates quickly (for example, behind loose non-western clothes in a hot environment)

Soap helps a lot, of course, but the usual stench of being dirty is more because we use really tight clothes that keep sweat from evaporating

[wizofaus]

Obviously it's not strictly essential at all, given how many 10s of 1000s of years humanity survived without it - but once invented among a particular population I would think its usefulness (for various purposes) would be obvious enough that unless the raw materials become impossible to obtain, production would continue.

[culi]

yeah for most cultures soap was probably used for cleaning other things first. In general it's a good way to loosen bits of dirt off of something. Very useful in making and maintaining fabrics. The idea to use them on our own skin likely came as a secondary innovation