Thank you!
We've added a Gained by section to trait tooltips after similar feedback. It'll be included in the next update. Some examples to make it clearer: If a colonist spends too much time idle, they roll for the Lazy trait. If they sleep outside they roll for Insomniac. Having low sanity for too long may also trigger rolls for random insanity traits like Naked. Number of traits is low for the moment and they become somewhat repetitive, soon there will be way more of them.
You can see the effects of traits by hovering over them in the colonist UI, but I also plan to add a Traits screen that shows all traits in a tree-like structure (in the future, maybe).
We've gradually replaced almost the entire old UI because it was taking up too much screen space. It was also a one-time job by an artist who we can no longer ask to make adjustments.
Btw, I've seen your proggy posts before and your game looks very cool. Good luck!