What's wrong with the gender neutral pronouns English already has? Why do some feel the need to invent new ones?

"It" is the neuter gender. "He" is masculine. "She" is feminine. "They" is common (masculine or feminine). The distinction between singular and plural is lost altogether in the second person, already blurred in the first person (sometimes people use "we" when they could really have used "I", and less often the other way around) and isn't doing much useful in the third person.

Anyway, somebody who calls themself "we" when they are just talking about themself cannot, by definition, object to being miscounted. But they might object to being misgendered. Best just go with the lesser of two evils.

Because, as you said, "it" is neuter, and the human beings who want to be called neither "he" nor "she" aren't "neuter"; they're agender or non-binary.

Back in the early 1970s the feminist movement wanted to get rid of what they saw as male bias in our language. Before that, words like 'his' and 'man' were used for gender-neutral language, as in 'mankind' or 'to each his own'. Feminists changed that.

So today you hear a teacher say 'Will every student pick up their pencil' instead of 'his pencil'. It sounds really dumb to me but we just take it for granted these days. Using 'person' for 'man' was done for a while--chairperson, fireprerson, etc.--but that didn't catch on. Now women WANT to be referred to by the male term--chairman, fireman, actor (instead of actress), etc.

There was even a movement to come up with neutral pronouns like Eis for 'his' or 'hers', and eir for 'him' or 'her'. Nobody liked that idea.

American English is officially defined by the way people use it. We don't have an official committee that decides which new words may enter the language and how people will use them, and that's fine with me. Our language is a growing, changing thing. And as soon as we decide how we want to say something, that's how it's said.

Pronouns are sexist

Special snowflake syndrome

'They' is a much better example of a gender-neutral pronoun than 'he'.

Because "he" and "his" are not gender neutral.

Yes, there is a convention that says you can use "he" or "his" in cases when the gender is unknown, however strictly speaking these are not gender neutral.