What you see as "free time" a lot of younger people wouldn't see as free time. I think generational differences are kind of overblown, but one thing Millennials do that actually is different from other generations when they were the same age is that they tend to view their job as a gig rather than a career. They have no problem floating around between different jobs or even making drastic career changes. They do this 1) so they don't get too tied into a job they might end up not liking and 2) so they have more time to devote to other things they are interested in, because they don't define their life by what they do for a living. On average, their career is not the most important thing in the life of a Millennial.
We view that as wanting more "free time," but Millennials don't think of the things they do outside of work as free time. They take their jobs less seriously than previous generations, especially Boomers.