Is it normal i don't want to clubbing for my friend's birthday?

I told my friend that I'll attend her birthday dinner but won't be going clubbing afterwards. She said it was cool but I can tell she isn't. Honestly, I don't care about birthdays and just see them as an obligation and therefore I no longer even celebrate my own. This is the first year I've told a friend I won't be joining them to go clubbing because I've decided to stop obligating myself to do things that I can't stand doing. I think people are upset because I used to be someone that liked that stuff before. But since I've had some changes in the past 2 years, people are giving me the stink eye. DAFUQ is up with that? I just want to know your thoughts because I've never been good at understanding certain things about people. I never obligate people or get mad about senseless things. I just don't understand these emotionally unstable people.

I'd like some thoughts, especially from the yankees.