The cultural difference of multi-stanning is really fascinating. In korean fandoms, multi stans are not “real” fans perse. They are respected but only as a person who multi-stans. To be respected as a fan of that group, it is necessary to keep to a single group. I can imagine a variety of reasons. Most communities form on twitter and naturally those who are only a fan of one group would prefer to see content within that group. So you curate your following accordingly.
In international fandoms, you are a fan of the collective phenomenon of kpop before you are a fan of a single group. Really its sort of understandable, the accessibility of kpop is vastly different in korea compared to outside of korea. It makes sense for those who find common interests in the big umbrella of kpop to flock together outside of the country. The result is the fact that i-fans are by vast majority mult-stans. Their enthusiasm know no bounds they cross from group to group and though they may have the “ult” (ultimate), it is often subject to change and their levels of affections are not notably different.