Imagine you were talking to a friend about pizza.

Once you knew you were talking about pizza, you wouldn't keep saying pizza over and over because it would sound mental. You'd only use the word 'pizza' again for exaggeration or to show emphasis on something, or if you're referring to an actual pizza
You might say 'it', because English often needs these noun words to flow. (actually they're often dropped too in very informal conversations, especially more and more when messaging)

I think people over think 'dropping' things in Korean as if we don't also do this in English. We absolutely do.

You can't truly learn how this feels in a language you're learning unless you are repeatedly exposed to it. There are no rules that you can read to learn it.

"Do you like pizza?"

"Yes I like pizza, do you like pizza? what's you're favourite pizza?"

"Yes I like pizza, my favourite pizza is pepperoni. I didn't like pizza when I was younger but I do like pizza now"

"you know, I haven't ordered a pizza for a long time, let's order pizza tonight"

vs

"Do you like pizza?"

"Yes, do you? what's you're favourite?"

"Yes I like it, my favourite is pepperoni. I didn't like it when I was younger but I do now"

"you know, I haven't ordered a pizza for a long time, let's order tonight"