Only conservative Christians normally tend to complain that the use of 'Christmas' is being 'prohibited,' because there's certainly no law against using it. But settings that want to make members of all religions or none feel more included and welcome, like schools, government offices, and large retail chains, now often tend to use a more secular term like 'holiday' or 'seasonal' instead.
Of course Christmas is already very commercialized, and winter symbols like snowmen, reindeer, holly, trees, candles, even Santa Claus, can be understood as relatively secular. So individual families, or businesses or churches or anyone who does in fact celebrate Christmas in any sense, are free to keep using the word and letting people understand it in whatever sense they want to, religious or non-.
Because the American holiday of Thanksgiving falls so close to Christmas (from a marketing perspective), ads often use 'holiday' to include both. There, too, we manage to be thankful for family, friends, and other blessings, without necessarily stating or agreeing on whom or what we're thanking.