Keynes was right on the fundamental analysis, but wrong on how much people appreciate the luxuries that the extra money from working three days more than you need to can buy (plus, something about the satisfaction that many people derive from working). Most people lower middle class and up could easily get by on 2/5 of their current salaries if they made the necessary adjustments to their lifestyles -- including moving to a low-cost probably non-urban area. But that's simply not an attractive proposition to most people.

Now, of course, there's a chicken-and-egg thing going on where two-day-jobs largely aren't on offer, but I'd argue that's largely because there just aren't that many takers. Especially in IT, especially if you're above-average successful, it's conceivable that you could find and negotiate a two day a week remote position -- but even among the population that probably could do that, it just doesn't seem a lot are, or are even trying.