List reasons why someone would have AnOther profile:

Back up in case of a ban.
An account where you can be more perverse or mean when the feeling hits and you don't want to tarnish your main account.

I don't have a second, but if I did it would be because I forgot how to access the first.

Your allowed 3 here if u so desire

They forgot the password
They are hiding from someone specific or caused too much trouble but don't want to leave the site so they pretend to be a new user
They think someone might misuse information they give about their life so they split it into several accounts pretending to be more than one person
They want to be both liked by most or at least stay neutral and express their controversial opinions at the same time
They play games with people

So they can message themselves and pretend they have friends

Could be lots of reasons. It's not my biz.

Some express things on second profiles that they don’t want the people they regularly interact with to know about. Like the funny ones expressing the difficult things they’re going through or ones who don’t want judgment expressing sexual stuff (or vice versa).

I have one floating around because I had deleted my account. I couldn't remember the username/password when I came back and made this one.

Because they’re being harassed on their main
In order to be fully anonymous

The first thing you listed primarily, I’m thinking

Because I can

So they can catfish themselves

Split personality? 🤔

Likely Trolling or other shady shit

Maybe for their alter ego

I have one to keep my other username.

forgot their password?