Why did the JDUBS have to question Christmas?

They used to celebrate it than I believe when Rutherford became President they started digging into it & decided that it was bad. Also I was thinking they claim Jesus couldn't have been born in December but he was born in the Middle East so I decided to check what winter is like over and it doesn't get to cold over there(someone correct me) so you know what he could have been! Why couldn't they question something else?