My guess is that we as humans tend to look at what we've missed out on rather than what we've gained. During Keynes's time there wasn't quite as much competition for one's time and attention, and whatever they had probably wasn't as cheap. Now we just have so much entertainment at our disposal that we can't feel satisfied with what we have.

I'll call it the Deal or No Deal irrationality. Essentially, if you go on that show hoping to win $1,000,000 but end up with just $100, you probably feel pretty disappointed. The $999,900 you didn't win ends up eclipsing the fact that you won $100. $100! A free night out with your friends! A nice fancy dinner! Who doesn't want that sort of bonus?!

[I might have accidentally stolen the above example from a Dan Ariely book. If I did then I do apologize]

Now in our society we have competing forces of remaining sociable, watching TV, browsing the Internet, maintaining hobbies, going on vacations, and (as the article notes) trying to work and more more in the process. I mean, I've had to sacrifice watching TV and playing video games just because I need to to have 'more productive leisure.' Board games, lifting weights, going out with friends, and programming are things that I like to do, sure, but that doesn't quite fill in the gap a video game may do in the same way. At the same time I'd like to do more biking and get into other more artistic hobbies, but the time cost to learning is so great and the ROI relative to what I already have on my plate.