Christmas is a very secular holiday. There is still mass, but in American culture the religious aspect of Christmas is minuscule in comparison to the secular and consumerism aspects. "Most of the songs are very religious" is just not true for most mainstream Americans.

For most Americans Christmas is about family, Santa (Coke's version), Reindeers, Elves, Trees, and Gifts. And then local or family traditions which may include mass, but for most, it does not.

If you'd like some stats - 90% of Americans celebrate Christmas. Fewer than half of Americans consider Christmas primarily a religious holiday. Among younger generations that is much lower (30% of Millennials consider it a primarily religious holiday). A majority of Americans say that Christmas is less of a religious holiday than it was in the past. Only about half of Americans will go to church on Christmas (compared to 82% that will spend time with family).[1]

https://www.pewforum.org/2017/12/12/americans-say-religious-...