Most of the time they become routine messages, often forwards that we receive from others, and with words that are not our own, nor from our heart. Very often people do not even bother to reply to such ritualistic messages which come in large numbers as a deluge.
I was recollecting once long back a friend had sent me a birthday card when my birthday was months away. She said that she is happy that I was born in this world and she could gain a good friend, so she feels like greeting me any time when she remembers me.
Gestures that are made when the other person is least expecting them have much greater significance, and they touch hearts.