Only the "interesting" button is relatively new.
My guess is that most readers don't click on the "warm fuzzy" buttons for one (or more) of the following reasons:
1. They got to the page, decided it wasn't what they were looking for, and clicked back out.
2. They have the feeling of "It's not my job!", or feel pressured and resent being asked to consider it, or can even become angry at the VERY IDEA!
3. They mean to, but forget.
4. They're just in a flat-out hurry or pressured by other concerns, and the time factor is very real to them.
5. They don't even notice the buttons are there. (Which may sound odd, but I'm one of those who did not even SEE that batch of buttons until just a few months ago. Some guys can have real tunnel vision! :)