I think I know why. I had a conversation with my roommate not long ago who is a declared atheist. I proposed that life is ultimately about lessons and learning. I was a little dismayed when he got a little condescending and implied that that was believing in a form of fantasy. There is no underlying purpose for the atheist. So of course well being has as much value as suffering if not more.
But as the C's have told us, we've chosen what they call the short wave cycle. (i.e. learning the hard way) Suffering is a far greater motivator for change and for learning.
It's interesting that atheist have a desire to be 'moral.' They want to take the moral high ground to validate their position. The rational goes something like this; We've got our feet on the ground. We're not delusional or hypocritical like those religious people.
My roommate feels it's important to be moral and just, specifically to represent being an atheist in a positive light.
IMO, what's funny about this is that they miss the point that in order to be truly "moral" and "just", you DO need to learn lots of lessons, thus making his argument false. You're not just born with it, and although you may have a "sense" of morality or justice, you need suffering, experience and learning to live as right as you can. It didn't fall from Heaven (certainly not for them, LOL!).
That's more like a PARAmoralistic stance, IMO.