Interesting observation. I think two factors come into play here:
1. We become habituated to our own discomfort. Abnormal becomes normal; self-defeating behaviors and patterns of thought become simply what we are used to.
2. People have a hard time dealing with the ambiguity and stress that comes from big changes. Even a positive change shakes up our sense of who we are and what we can expect to varying degrees, and that is stressful for anyone. We tend to resist such changes even when they are useful, because even a positive adaptation demands energy. It's just like adopting a healthy lifestyle after years of being a sedentary chain smoker surviving on coffee and cupcakes - the challenge can be that significant.