Someone said :
She'd still be famous. Sia has been around since the nineties has written, produced and sung some of the most interesting, intelligent beautiful pop music that exists and created some of the most interesting, intelligent beautiful music videos. She has also been a hit factory for other artists. This is I'd guess and having listened to her explanations more of a sort of quirk statement than a genuine attempt at 'not being famous'.
I think it's a quirky move from her. She did say on Graham Norton that she feels "bratty" doing it but so what!! She is an incredible talent so let her do what she wants.