I can see what you are saying, but not every office needs an oath. Kings, dukes, maybe heads of guilds/religions. The rest can be implied oaths of fealty, but leaders need to be bound by some memorable promise.
All it really amounts to is a copy-paste from a text-file, so it isn't too laborious. People may get mad more vehemently when those promises are broken...which is good and bad.
People have a tendency not to bother with these things unless they feel pressured to comply. Which requires, usually, at least one person who cares enough to exercise this pressure. I have seen a number of such oaths or constitutions fall into disuse, over the years, as the number of people who cared enough waned.
I agree with what you are saying, though. While applied, their disrespect does tend to increase discontent.
But that discontent is also relative to the number of contenders. If there were five candidates to rulership, all vowing to respect a given oath more piously than the other, then breaking the oath would likely upset quite a number of people. If there was just one candidate, and he never even pretended to care about the oath and didn't even bother formally giving it, the discontent effect will not be great. And as the game is evolving, well, the number of candidates in any given situation is constantly nearing zero.
