The problem is who you are thanking. Holidays like Thanksgiving and Christmas interfere with their desire to enforce atheism.
You've nailed it.
I also find it annoying to see an ad for something substituting the word "Christ" in "Christmas" with something else, the name of some product they're trying to push This Holiday Season.
I love Chex party mix, but honestly, "Merry Chexmas"?
My wife and I noticed it on the Food Network when all the shows talked about "Friendsgiving" and scarcely mentioned "Thanksgiving". I had to look it up. It is supposed to mean Thanksgiving with friends rather than family. Sounds like BS to me. I think that Thanksgiving celebrations have almost always involved friends as well as family. It can be "Thanksgiving" whether one is with one's family or friends (or both).