Ergo (roughly speaking) you're asking employers to cut cumulative productivity 20%, and thus revenue/profits 20% for ... what? while other employers race forward with "100%" employees, producing 25% more per week.
40-50 hour weeks seems about the limit before employee productivity & availability ends. Claims of how productive ("refreshed! rested! alert!") employees are on shorter work weeks doesn't translate to comparable results, i.e.: 80% work time doesn't produce near 100%.
My personal goal is productivity. Give me more time at home, yes, I'll be productive there ... but I can be more productive via an employer (that's why I'm employed) than growing/building what I need on a farm. Cutting work hours means less work getting done, both for my own ends and my employer's bottom line.