An answer would be that the Federation didn't render assistance to the Klingons and that the Khitomer Accords was really nothing more than a truce between the Federation and the Empire.
I don't think an actual alliance between the Federation and Klingons came about until after the Narendra III incident, but both sides reserved the right to withdraw from the Accords.
I suppose that could in fact be the case, as it is unclear (canonically) if the UFP did anything to assist the Klingons. But it does make sense to me at least, that the UFP would have done
something to help the Klingons recover.
The Feds will pretty much any planet (so long as it is within the prime directive) that was in a similar situation, if assistance is asked.
It doesn't make sense to me to simply sign a peace treaty with no other action on the part of the Feds, just because Praxis blew up. The Feds were a defensive force, and although there were some "hawks" advocating for bringing the Klingons "to their knees," that wasn't the mainstream ideology of the Federation and I don't think the UFP would have invaded the Klingon Empire, even without the Khitomer Accords. THat's what implied to me that the Feds provided some form of help to the KLingons, along with signing a peace treaty.