It would be handy for people to move their own threads into different sections, but as Walrus has already mentioned, people could easily abuse this power by possibly spam moving their thread or continuing to move it into another wrong thread which could possibly lead to a punishment ( I could imagine that sanctions would be put in place for those who troll with the move thread function ). So I guess the main reason is the Community Lead Team don't want people who are possible distrusted moving their threads and want someone a lot more familiar with the Forum Rules to do it instead, this way we/they won't have to deal with rule breakers minging with the function.