@Riger Keep in mind that the Fae aren't human, so it's a bit of blue and orange mentality in this instance, though the reason it remains popular in fiction is the traditional belief found in many cultures about the importance of a person's lineage. Imagine fucking up so bad you get your line cursed for generations and, since this generally goes hand-in-hand with the belief in an afterlife, having all eternity to be tormented by your ancestors
and descendants.
In this specific case, I think the length of the curse (about 10 generations) could be viewed as the direct descendants (so the king's children and grandchildren) feeling angry at him for getting them cursed, but maybe feeling he was justified; could also be some shame at his hubris, but I wouldn't count on it, since the family we've seen has done nothing other than try and weasel their way back into having access to the spirits' powers. Anyway, after a few more generations, it just turns to resentment at not having that power, making them even
less likely to try and make amends, which makes the spirits feel more justified in their wrath.
And, to be fair, they're not exactly wrong, seeing how the dude basically committed a minor genocide against the people he was going to for help, probably with the approval of his people, since that's not the kind of thing one person could do on their own.