There are two potential reasons for why the Duggars don't have a Christmas tree. Some conservative Christians want there to be a focus on Jesus during Christmas, which means no Santa Claus or Christmas trees, neither of which have anything to do with Jesus. The other reason may be that witches came up with the idea of decorating trees. Witches are often associated with the devil, so the Duggars try to stay away from anything that has to do with witches. It would be very hypocritical of them to not celebrate Halloween because it was created by witches but have a Christmas tree, which was created by witches.