In spite of positive job growth in the U.S., “the percentage of working-age Americans in the labor force remains stuck near its lowest level since the late 1970s. Although retiring baby boomers are the main reason, there’s another troubling factor that experts predict won’t be solved by stronger economic growth. Too many men in their prime don’t have a job and aren’t even looking for one. Experts trying to figure out the reasons are probing the roles of criminal background checks, painkillers and even video games.