Yes, because I want it and it will be mine. Also, if they're really that useful they deserve to be taken down a peg.
I guess technically none since there are only two examples here for such long lasting alliances and it took more than a day to communicate between France and Scotland or England and Portugal.
There are many more alliances that lasted quite long periods of time. The Franco-Ottoman alliance, for instance, lasted 250 years. It literally took the largest revolution of the EU era to break it. The number of alliances that broke over territorial disputes, particularly minor ones is exceedingly small. Most of the time alliances lasted until the common threat was broken or neutralized (or one of the participants was decimated).
The real problem is that the AI is terrible at weighing risk vs reward. Rarely does the AI have a new alliance partner lined up; for all the musical chairs of western alliances is was
extremely rare for even perfidious England to break an alliance without having a backstop. Sure they might stop supporting Austria and instead back Prussia ... but the AI
does not do this. The AI routinely goes ballistic over extremely minor territorial items and they do not adjust their foreign policy, they just say "whelp time to throw away my game".
This is a problem throughout the game, the AI does things for "reasons" which hurt it and make the game easier. Who your allies were have always been far more important than minor territorial concessions.
If you want a backstabbing AI, just make the AI backstabbing. Do not have some opaque mechanism that leads to the AI having inconsistent priorities.