By that logic, you should be enforcing a 60 hour/week, to achieve even better goals.
The problem is that job != job, because different jobs have different requirements.
A doctor needs to be available continuously, but he doesn’t necessarily need to be working continuously. An on-call doctor needs to be available 24/7. A general practitioner may only need to show up for scheduled appointments in strict timeslots.
A programmer on a long term project needs to eventually put in hours, but precisely when he puts in those hours matters less. A senior developer is productive anytime he’s available for advice (and there are others working to be advised — with off-shore resources, this can mean extended availability)
A warehouse worker is productive only when he’s explicitly doing labor. Being available for labor, but not doing any, is worthless.
A programmer on a short term or last-mile phase of a project needs to put in the hours, but on a strict timeline — there’s no room to skip a day and make up for it tomorrow.
Companies already acknowledge this, albeit implicitly. The higher you are in the hierarchy, the more valuable your availability and the less your labor. CEOs don’t get to have strict no-work vacations, but they also don’t have strict 9-5 work/life split, because they need to be available all the time. At the same time, they can go normal days without any real work to do, because they aren’t needed for anything.