I do not believe that business owners are trying to maximize the efficacy of their resources. If it were so, this kind of proposals would be accepted by the business community, given research on the topic. I believe this proposal is a tremendous opportunity.
I believe business want to control people. As such, one less day is less control. In exchange for Business controlling your life you get different degrees of financial security. Feudalism.
This attitude is reinforced by tradition and misconception. And both employees and employers are at fault. Gee, I am at fault! I haven't worked a 40 hour week in my entire working life. On my defense I would say that I have sent juniors and interns home... But still.
I have also said that research on the topic is not solid, but of this proposal were to be properly implemented could help solve that issue.
Politicians doing a proper policy implementation is a different can of worms. I was hoping that some progressive business would actually start doing 4 hour weeks, rather than a top down approach.