I don't think Admins have been involved
If two of them are banned, all that's needed to get the rest banned is finding evidence of ban evasion.
If they reused the same addresses or social media accounts in bounties in the past, that shouldn't be too hard with Ninjastic.Space.
So you are saying that I can create alt account and post exact same sentences or posts, and this won't be considered as plagiarism?
If the account is a known alt of yours, I don't think that would get you banned. But it probably goes against rules such as spam and low-effort posting. Low effort because all you are doing is copying your own posts and posting them again. If no one knows the other account is your alt, it could get banned if reported and admins decide that's the correct punishment.
Wikipedia definition for plagiarism is saying that even using other people language, thoughts and ideas can be considered as plagiarism.
Yes, but the emphasis is on other people's. Stealing other people's posts, ideas, thoughts, etc. If those accounts are alts, they aren't taking anything from other people.