there is a lot to be said about the idea that being too open about these things is a social vulnerability. declaring who your enemy and friends are is quite useful intelligence to someone wanting to sow discord. so i get where it originates, and my speculation is that it relates somehow to the codes of shinto.
i wil sound like an idiot trying to articulate it, but i think the differences between simple text emojis favored by asians in general, but especially japanese, in contrast to westerners, illustrates it:
>_< ^_^ versus >:O and :) <:
the eyes are the focus in the east, the mouth is the focus in the west, westerners are more prone to being loud and unsophisticated in their expressions. russians also are not prone to smiling very much, and keeping the emotions muted in their expression.
anyhow, i know that japan has a disproportionately large number of nostr users, and relays, and they are mostly insular. this again points towards that valuing of privacy and discretion. and probably why nostr is so popular there, as well, because it means less surveillance by the platforms.