But they all should have given reasons from square 1.

Facebook gave reasons for some bans (like nudity).

But, none of them afaik have ever really had a route to talk to a human & get reinstated.

I know Twitter recently has. I opened an alt when E bought it & got banned on signup (nothing offensive, just a plain Jane new account). I wrote to them and asked what was going on & why was I banned as the news feed was first loading.

They (a person) responded, apologised and reinstated immediately