I think you are missing an important dimension of this issue:

There are many professionals who work more than 40 hours, many of which are providing visible output to the company.

Perhaps that work structure could be refactored to require fewer hours and deliver the same corp value, but there is a competition WITHIN each company between the employees of those companies. This drives work aimed at bettering ones relative position at the company and (sometimes) only secondarily provides actual value to the company.

Of course companies want to minimize this, but it is challenging as employees are inherently incentivized to game this system, and they have all the time in the world to strategize about this.

The result is a pretty competitive work place, and many more than 40 hours naturally worked, not because of any gov or corp mandate, but rather because they are maximizing corporate position.

~

the second issue at play is the value of centralization. One person owning a thing is often better than a committee. Thus the higher one goes in a company, the more value a company gets from each additional hour provided by that high level person. Since people want to be higher level, it puts a premium on willingness to "kill it" both in hours and tempo.

I work in silicon valley. Fast movers are very valuable, but this reality puts pressure for everyone to appear (and be) this way.

I dream of a world where folks work intensive periods with large breaks. I think it could be effective, but I don't see it happening w/o some kind of forcing function.