@Goyal99Raj The king did say the kingdom will be looking for a way for the heroes to return home once the demon king threat is over. Whether that was a lie or not, is unknown.
The problem with Rose's approach, which you described, is that Usato (like the other two) have got absolutely nothing to do with this particular country, in fact not with the whole world. Not a perfect comparison, but it's a bit like a European or an American tourists visiting China, to see the museums and other sightseeing spots, would suddenly be snatched by the Chinese military and put through hellish training in order to defend Chine against its enemies.
When a person joins the military or is drafted, they at least know they are working for their own country, their own family, and ultimately themselves. Unless it's a total dictatorship in which they live. Japan, obviously, is not.