Before reading the article, I would guess it's because they can't or won't do anything for themselves - always counting on others to take the lead.
Scholars on both the left and right have studied this question extensively, and have reached a consensus that it is conservatives who possess the happiness edge. Many data sets show this. For example, the Pew Research Center in 2006 reported that conservative Republicans were 68 percent more likely than liberal Democrats to say they were “very happy” about their lives. This pattern has persisted for decades. The question isn’t whether this is true, but why.
If you want to find out, go to Why Liberals Are More Likely to Be Unhappy People | John Hawkins' Right Wing News