ummmm..good question our new Fluther member!
Probably because of several things. First, many family members are jealous of one another. They love to point out your shortcomings to make them feel better about their miserable state of affairs. And, mostly regardless if they are family members or others, there are some mean-spirited people in the crazy World.
During the holidays, these feelings really surface due to stress. Everyone is out of their “comfort zone!” Too much to do with to little time to do it.
My philosophy, be nice and smile!