For many assimilated Jews, I think that celebrating Chanukah, even as a substitute for xmas, shows the last remnants of their Jewish observance. It may be as minimal as buying a Chanukah present for the kids and not a xmas one. That's even easier than buying a box of matzah and making some effort to hold a "seder" on Passover.
Over the years when various relatives married non-Jews, if a female relative married a non-Jew I'd buy them a present, a Chanukah Menorah. Sometimes I got it for a Jewish couple, since it seemed like a nice Jewish gift from the relatives in Israel. I don't know how many actually have used them. I certainly don't ask.
But if I'm not mistaken, it's the one ritual item most people are familiar with.