Eli5: Why do you use “they” for non-gendered speech instead of “it”?

Question

I’m not a native speaker, but as far as I understood, for singular objects and animals “it” was used. Why use “they” for individual people then?

In: 1400

Answer 1

Because grammatically “they” has been a correct term for a singular person longer than the word “you” has. Since the 1300s.

And because nonbinary people are not objects or animals. They are people.