I don't think it's possible to pinpoint why relationships dissolve. Sure, there is always "something," be it dirty dishes, a certain habit, etc. But usually, these are context-specific complaints, meaning the person complaining about e.g. dirty dishes could be happy in a totally different relationship where their partner also didn't do the dishes. Ultimately relationships break down because one or both people stop trying. Caring about the dishes is a symptom of, or response to, relationship apathy, not the cause.