What about my alcoholic friend I've known for 20 years that is destroying his life and lashing out at me right now because he is sick? Or my heavily depressed friend of 30 years who I sat with on the weekend? Not everything is about extracting maximum personal happiness. Friendship can also be about service.
If you care about these people then presumably it does make you happier in the long term to let them know that you care about them. Especially if it's not that pleasant in the moment I imagine having a system to remind you could be helpful.