Receiving a holiday card is probably like receiving a gift. You appreciate the thoughtfulness of someone giving you a gift, but you really appreciate a gift that actually acknowledges you individually. E.g. your favorite color, drink, candy.
So if you don't celebrate Christmas and/or aren't Christian and someone gives you a holiday card that says Season's Greetings, Happy Holidays, or Happy New Year, you'd probably be touched by that thoughtful consideration.