This is an artificially induced mechanism that isn't logical. Treaties are agreements that can either last forever, expire, get cancelled or be ignored. Agreements are not tangible things that can degrade (except the paper on which it's signed).
If the purpose for this is to promote or reduce a justification for acts of war (casus belli) through the mood of the populace then relations would be a better idea. Relations are tangible in the sense that it can be observed in people's attitudes, feelings, etc. Relations between realms can improve or degrade. The people can either start to demand war or peace and if denied, region stats could drop or revolts could occur.
The current idea that treaties need to be maintained jars the senses.
I think the idea is that treaties can be overcome, gradually, through red tape.
RL example: Free trade agreement is signed. Yay, we can trade freely! Of course, the Consumer Protection Agency wants the childrens toys inspected for lead. And of course, the company doing the importing should pay for the inspection, right? And then we need to scan the containers for nuclear weapons, so let's tack on a $50 "security charge" to every container, to pay for the guy to run the scanning equipment. Pretty soon, the 'free' trade agreement is costing companies in the other country more than they would have paid under the tariff system that was in place previously. Treaty is, for all practical purposes, destroyed.
