I thought the idea of Meta-MSE was to help MSE users. Please could someone explain to me what I did wrong by asking this question I thought careers/study advice was off topic. It has received 6 down-votes and 3 votes to close with absolutely no explanation for why it was a bad question for me to me ask.
I wouldn't take the whole thing too seriously. I don't think you did anything wrong, and even upvoted a while ago (and I'm agnostic about whether the "powers for good" question is on-topic).
Whether that particular question on Main is on-topic is clearly a contentious issue -- some people want it closed, others want it open. Given that votes on Meta can quantify agreement/disagreement (rather than appropriate/inappropriate), it's entirely possible that more people who cared enough to vote wanted "powers for good" open and downvoted to disagree with your (perceived) desire that the question be closed. This is supported by the fact that the question is currently not closed on main last I checked; the "close it" crowd are ... in the minority, or something.
If that is the case, then downvotes certainly don't imply you asked a bad/inappropriate question. I gather that at least two of the three close votes were from before you expanded the question a bit, but even then, it seemed clear to me that you were just wondering why it is (perhaps implicitly) considered on-topic. In other words, I personally don't really agree with the close votes on your linked question.