An in-universe explanation I think that is implied is that Quonos was doomed if Federation assistance wasn't rendered, but the Kitomer Accords provided for that.
The real question is why does the Federation keep saving the Klingons, only to have them forget a few years later, and become the UFP's enemies again. For example:
Archer and crew saves the Klingons from the augment affliction, yet how do the Klingons thank Earth and Starfleet? A cold war that lasts pretty much until Star Trek 6.
The UFP saves Quonos, as per the Kitomer Accords, and you would think THAT would make the Klingons eternally grateful. But no, they have cool relations all the way up to Narendra 3 incident, in which the Enterprise C is destroyed trying to save the outpost. In fact, in the alternate timeline, the Klingons end up declaring war on the UFP.
In the prime timeline, Klingons throw a 20+ year alliance down the drain simply because the Feds refuse to support their dubious war against the Cardasians. In fact, they declare war on the Feds, as well, and the two powers fight a short but bitterly fought war.
And if you count STO as quasi-canon, 20 some odd years after Nemesis, the Klingons go to war with the Feds yet again.
Not to mention, the Klingon Empire is generally one ruled by terror and through conquering and exploiting other worlds. Every Klingon from Star Trek 3 on is portrayed as a bloodthirsty bully ready to pick a fight with anyone weaker than them.
Maybe Kirk was right when he said "Let them die!"