There is a slice of life slow life story that is neither a romcom nor an H where the MC gets a harem and has the girls...
It's just done casually....
If authors are going to add the option, they should do it.... if not, just don't add the harem option.
Hell, you can still make him desirable without giving the harem option... just claim any woman is willing to be his wife and that he could pick any one....
This series is not optimized for logic. The story is created for the target audience and then explained in story why things are like that afterwords (at least they
try to explain and make it seem natural).
Wanting a harem is a fantasy that the target audience tends to have, but having one is unrelatable. It also conflicts with Japanese common sense, morals, and decency ideals. It is kinda like the logic of why hentai authors halfheartedly censor their own work.
It was never about a logical reasonable flow of plot development and world building. It is about how much they can pander to boost sales w/o being censored or change demographic rating.