Is this because I was a JW? Or a pessimistic/over-thinking personality trait?
Its both! I went to a seminar years ago where ex-cultists gave talks about their experience of leaving. A woman from the Children of God said just what you're saying, small talk seems well - small! She found that the way people lived seemed pointless, she desperately wanted to find the meaning.
It's because we've come out of a cult where everything meant soooo much, everything you did, said and even thought. It was the end of the world, well soon! We had lives to save!
Its not, actually, over-thinking to want life to have meaning but you've got to find your own meaning, what matters to you. Whether it's art, science, sport, music, literature, travel, relationships, Netflix or whatever. Don't think that the pursuit of happiness doesn't matter, it's vital to your health and well-being. Good luck searching for meaning and try and enjoy it. 😀