People in the middle ages in Europe often used hardwood ashes (potash) for cleaning. When mixed with a little water you get lye, which does an OK job at cleaning (and will even make weak soap spontaneously when cleaning greasy pots or your skin).
It's not that soapmaking was unknown. It was that it was associated with Jews, and thus unacceptable (which makes about as much sense as any aspect of antisemitism, I guess). England passed heavy taxes on soap because they knew it would target Jews while leaving the English alone. So just because a technology might be primitive, it doesn't mean that there can't be other reasons why it's not done.