Probably to make a few more creative maps? I know the third-party wm_siberia map has both rain and snow, but like it's been stated before, the sdk 2007 weather effects are bad, which can be seen in that map. The snow isn't that bad, but the rain isn't good either. I'm assuming sdk 2013 has better weather effects, and since v4.3 is supposedly going be on sdk 2013, maybe then there can be better weather effects.