We don't believe so.

Like many holidays that were once rooted in religion, they eventually become secular holidays. For Christmas in particular, it is actually not even Christian, nor is it required to be religious. Many Christians barely even make it a day about Jesus[1].

The roots of the holiday are that of a Solstice celebration - the point in Earth's revolution around the sun (Although they probably didn't understand it as that at the time), where the days stop getting shorter, in the depths of winter, and start getting longer. After the solstice, the season marches towards spring.

The Christians integrated this holiday with their own celebrations[2].

Additionally, many current atheists are "Cultural Christians", "Cultural Jews" or "Cultural Muslims", because that is the way they were raised, with any related holidays included. They continue with those holidays because they enjoy them.

It is not uncommon for people to celebrate holidays from cultures whom they are not members. It is about having fun, and there's nothing wrong with it, even if they don't accept the mythos from which those holidays came.

To qualify has hypocrisy, atheists would have to be taking actions that were contradicting their position. Celebrating a holiday that does not require or acknowledge a god does not constitute a contradiction.