"Pain and negative emotions activate the reward centers of the brains causing unconscious addiction to those negative emotions." Negative emotions light up the brain, activating the beta-endorphin and dopamine pathways, just as cocaine and another narcotics do. Consequently, people can easily become addicted to those emotions physiologically.
While there are a number of theories underlying addiction... some psychological, social, biological and the like... one thing is clear, underlying all of those theories is one physiological truth, the release of opiate peptides which are naturally secreted hormones in the body that create a "natural high; These are the runner's high hormones.
Other theories are that, the negativity taps into things like:
-the need for attention, the inability to give or receive positive attention, the generational and entrainment to focus on what's wrong and of course, the simultaneous feel bad coupled with the "feel good" which is the attention we get from feeling bad.