I don't know why the tradition of sending "Thank You" cards or notes is dying, but it truly is not fashionable or trendy to express gratitude for a gift.
I will be the first to admit that some of the gifts that I have received in my life were not desirable, but I have always appreciated that someone thought of me and took the time to present me with the gift. A written a note of thanks or gratitude is sent within a week of receiving the gift.
I've noticed in the last decade that more and more people (family and friends) don't bother to acknowledge a gift - wedding, shower, birthday, birth, Christmas, and other occasions. Sometimes, if it wasn't for Delivery Confirmation, I wouldn't even know if the gift was received. I find this trend unsettling.