It was closed because it's been cross-posted, and there's no point in having questions accumulate answers on both sites, where they diverge and the information is spread across the whole Stack Exchange network.
I actually left a comment on the very same question:
I'll have to close this here since you've cross posted. In the future, please only post your question on one site where it's on topic. Thank you!
To address your specific concerns:
It does belong here!
So it does on Ask Different. It's for the OP to choose.
2 HOURS after I post my answer, one is posted on AskDifferent (likely by copying my answer).
Please back up your claims about the answer being copied. I see no verbatim copies, and one would assume the common solutions to a problem always go in the same direction. Even if it were so, material you post on Stack Exchange sites is free to be used by others here, even copypasting it is not forbidden per se.
How does this benefit the SuperUser community?
It's there to prevent two questions existing at the same time on multiple sites. If Ask Different had seen it first, it'd probably be closed there as well.
You don't want two versions of the same question move into different directions, or even in the same. For example, it takes so much more effort to answer two versions of the same question – especially if you need clarification and have to ask for it, when the OP might have given more details on another site.
Why don't I deserve to be rewarded for the time I put in?
You do. You're not punished, are you? Maybe we can migrate the question to Ask Different and have it merged, if the OP agrees.
What is the reaction going to be of the person that asked?
Let's hope they'll understand cross posting is not allowed and that in the future they'll know to post only on one site.