The bargain chip is weak. They assume the man will care for his girl and they assume no accidents will befall upon the girls forever. There might be more to this.
Kinda crap, but at least the author isn't trying to be ambiguous regarding the summoners' intentions, I'd rather an openly-evil kingdom over yet another "the kingdom is secretly evil uwu nobody would ever guess it even though it should be obvious to anyone with two braincells to rub together"
At least this garbage fire isn't trying to hide that it is trash. Between Gun-Ota's artist and his broken neck characters and the stupid premise of holding girls hostage as slaves, this thing is either going to burn out in a single volume or go on for sixty chapters.
I bet that in less than five chapters it'll come out that even when a student meets their quota the girl is still going to end up getting raped/humiliated. Probably while they are out hunting monsters at that.
That's the reason the isekai manga Wortenia Senki starts in a gorey way, because he was going to live something similar those classmates encounter, a worst posible isekai situation with nice freebies, they will live in a circunstance of "welcome to volunteering slavery hell with benefits, just don't break the rules and everything will be fine"
BTW there is something similar but more taking the worst of this manga, in that one the MC don't care a shit about their classmates (mostly the girls, that are treated like used condoms the rest of the world and their classmates), make narcissist monologues, and its too edgy to feel something different of wasting time
The shitty manga is called "Astro King - Summoned as a Hero, I Turned Out to Be Low Rank, so I Made a Maid Harem!"