They already know that a) MC is an unique existence, and certainly far more powerful than anyone on their side, hence why they need him, b) MC is extremely hostile and willing to kill if provoked, and c) MC lives within a barrier that not even royal treasures can break through.
So what exactly is the fucking point of a public bounty? Who the hell are they even trying to attract? If there is a bounty hunter skillful enough to break into MC's home and either deal with him or capture his woman, then why not just recruit that guy instead?
It would be fine if they tried to get the girl using like secret royal spies or some shit. At least that would mean they think they can covertly get past him. But making your intentions public knowledge is beyond braindead.
I know this isn't exactly high level literature but holy shit, the author didn't even try. This conflict is so fucking forced.
It's probably written to show that they know he's powerful but uncertain as to
how powerful because... wiping a kingdom off the face of a map kind of doesn't leave anyone alive to tell does it? Maybe people who fought in the same battles (I'm not saying along side him because I get the feeling the author is trying to say that kingdom didn't want anyone close to him).
Also to note the majority of characters who have underestimated him that attacked or made demands we either very stupid nobles with a obvious lack of awareness and social knowledge other than simple bootlicking. Or dirty vagrant "adventurers" trying to win it big with only knowing that he is an "evil" being that will make them a hero and rich at the same time.
So while they know what happened they don't specifically know
how or why. Ivern and Yuria quickly abandoned trying to kill him not only once he beat their asses but when they heard his story, and I'm guessing he's not willing to tell everyone that comes looking for him about what happened due to being fed up with this world that kidnapped and betrayed him.
The two princesses came with Similar knowledge. However unlike the 2nd princess who assumed anyone with a weakness or desire could be simply pulled under to serve for it is her "birthright" to rule and "destiny" to be on top. whilst the 1st had a more realistic reaction in discovering not only how strong he is but is now under the impression of realising how fucked the whole situation is and that there's nothing to gain by pushing further.