I am making this example based on some Japanese I heard about a different subject, but the basic context is the same.
The context is that someone has lived in a fishing village for a long time. As a result, they have eaten many types of fish:
"数年も漁村に住んでて、いろんな魚種類を食べてるのだ。"
however, I would say it without "のだ":
"数年も漁村に住んでて、いろんな魚種類を食べてる。"
So, is it like a native speaker will not feel an implied causation between (1) my having lived in a fishing village for a long time, (2) I have eaten a lot of different types of fish unless I attach the "のだ"? (1) and (2) could be completely different thoughts in the same sentence?
What I mean by implied causation is as such:
Having lived in a fishing village for several years, I have been eating many types of fish.
Because of the implied causation, I don't need to say
Because I have been living in a fishing village for several years, I have been eating several different types of fish."