More people, more hours: more coal extracted.
Interestingly, farmers in the middle ages are a much more balanced model (catastrophes aside): the land they had was mostly manageable by a small group of people, and there's only only so much you can optimize, given the patch of land that you have. So you do what you have to do and when you're done, well, you're done.
Personally I believe in remote and that it will get even better as tech to facilitate it improves.
I don't believe in working 4 days for engineering specifically. The field changes rapidly, there is a large learning curve and it takes a lot of hours to really master it. There is also some fixed overhead in communicating with other departments which stays the same even if you work less hours. So you remove more than 20% of your productive hours with this approach. You also reduce the time you spend learning. This further hampers your productivity. I think it will be a niche thing only done by some startups that care about this, have no other way to attract talent and aren't very ambitious.
That being said, for some people it will work well. It's pretty common for some roles in the netherlands for instance.
Or why people keep using it?
I refuse to refer to people as resources. I won't willfully dehumanize people by treating them as raw materials or as machines.
I've worked remote and managed remote teams for many years.
Working remote definitely doesn't not make "most people" more productive. Some people are more productive remote, but the average person gets less done even if they work more hours when remote. It takes a lot of training, mentoring, and performance management to get them back to in-office baseline.
This is regarded as a feature, not a bug.