@Wildstag The isekai characters seem OP but not driven enough to take over or reform a country, and there's little incentive to do so rn (they all seem fairly ignorant of either how the world works or don't care). If the imperial family gets their own powerful servant, then their own host families won't be under as much political pressure from the imperial family, and the imperial family can take action without having to call on one of them.
At least in Sansui's case, he's lived so long he really only cares about his adopted daughter and going against the imperial family (after they just secured her safety from the other country) seems irrational. Plus, the berserker girl would be annoying to the other isekai kids too...I mean the only other option here is to kill her, bc she clearly would go after the other isekai MCs after hearing they're also hugely powerful as well.