Why are so many people commitment phobic?

I get that not everyone is cut out to be in a relationship and it’s sometimes easier to have casual sex. I get it that some people experienced terrible trauma or abuse. But these exceptions aside…

there are way more people that are single than are in relationships…and these aren’t people in their teens and early 20s. I see so many people like this in their late 20s, early 30s, and mid 30s as well. This also isn’t a oh he or she is ugly and can’t find anyone. I see lots of pretty girls and good looking guys with great jobs, good families, etc. refusing to commit to anyone and play around the field or get so consumed with their career or friends. You ask many of these people they say I’m not feeling the chemistry or I’m having some form of self sabotage. What is up with all this nonsense? It’s called life is hard, stop overthinking everything, and grow the fuck up.