No, the answer is not just “video games are fun.”
A draft paper made available by the National Bureau of Economic Research, a clearinghouse for working papers in economic research, links at least part of this difference to video games: Statistical modeling by the authors suggests that young men are working an average of four fewer hours per week than they once did and spending three of those four hours playing video games.* The gaming doesn’t account for the full difference in workforce participation between younger and older men, but they estimate that it accounts for between 38 and 79 percent of that variance.
Source: Why young men might be playing video games instead of working.
Geekhammer 