That much is completely obvious; I don't think anyone is arguing that Craigslist don't have that right.
People are annoyed because shutting down PadMapper (without any effort to provide similar functionality) is a shitty thing to do. PadMapper was a useful service; now it is not useful. That is unfortunate.
Personally, it also seems hypocritical for Craigslist to claim that they just build what their users' want. I think it is hard to argue that shutting down PadMapper is consistent with that goal.