My question was converted to a Community Wiki by a mod, why did they do that?
The most likely reason is because the question is one of the following:
Quotes from the Stack Overflow Team
Well said. The most gratuitous example is probably "favorite programming cartoon". Is it appropriate for someone to get 1,000+ reputation by posting their favorite XKCD? They didn't exactly do anything... – Jeff Atwood♦ Mar 29 at 3:42
To mitigate the large reputation gained from relatively little contribution in content, we ask that "list of X" (i.e. poll-style) questions be made community wiki from the outset. – Robert Cartaino♦ Jul 2 at 23:46
the more a question produces answers that are not original content, the more it should be cwiki. we explicitly discourage answers that are simple links, or trivial cut-pasted content. We want original contributions. Tell us what YOUR experiences were and how YOU solved this problem. – Jeff Atwood♦