He has done a couple times before. I don't know why he does and I don't know why he unprivates it either. I don't know for sure but I believe that, while Steven has carers, because he is not in any form of institution or similar controlled care facility they are not allowed to control his life in those ways. Same reason they can't stop him from wasting his money on babestation calls and porno vhs tapes. He has been judged competent enough to live alone and thus make his own choices, which for the record I do agree with and I believe he is mostly able to do so successfully. But those choices including managing his own online accounts, the carers can suggest him to private things and try to explain trolling and so on, but they cannot force his hand and even if they do convince him to private his account they are unable to stop him from undoing it later.
Not normal enough to not be trolled but not retarded enough to have someone step in to stop him being trolled.