We love to be miserable. Not really: we actually tell each other, and ourselves, it's miserable being miserable, but that's the point: we're only adding to that state of what we love.
Misery, melancholy, sadness, tragedy - why is it so much more meaningful to us to be within these states of minds, as opposed to being happy or fine or just in a good mood? The latter are so much more transient and we acknowledge that they aren't likely to last before the former comes back. And yet, it is our self-professed ambition to achieve the latter.
But really, we kinda revel in being miserable. It's a channel of its own where we can express whatever negative energies in an act that is actually an expenditure. Through the act of synthesizing these energies we achieve paradise through catharsis.
If we don't have this up and down motion, we don't feel like we're moving. The dynamics of emotion remind us that we are alive.