I can see one reason: the benefit that you get from an activity is a nonlinear function of how much time you invest in it. This is why people tend to specialize in certain domains. If you barely have any time to practice painting for example, maybe it's not worth learning to paint in the first place. Conversely, if you have more free time, it could be worthwhile to find more creative things to do with it.
This is especially true if you consider frame-switching overhead. The amount you can get done in 6 hours of some demanding creative activity is probably more than 3 times the amount you could get done in 2 hours. And obviously people would have more long uninterrupted blocks of free time if they had to work less overall.
Also, with most schools being the way they are, I think children in general get very little opportunity to pursue their creative impulses; it's always about following the teacher's instructions. Maybe adults would have more curiosity and creativity if these traits weren't snuffed out in their formative years.
Finally, even in our current society, being just a lazy consumer in your free time is far from universal, for example: https://www.namm.org/news/press-releases/gallup-organization...