Why do so many Chinese students enjoy celebrating Western fe

since when have Chinese begun celebrating Christmas Day?What do these people celebrate it for,the Birth of Christ?But we all know that most of Chinese are not christians,they don't even know the origins of Christmas Day,and they celebrate it for no reason。anyway I can't get reasonable answers from my friends,some of them think they would like to just take this chance to enjoy themselves regardless of the meanings of the festival。