I want to start by saying I know this doesn't apply to all jobs. There definitely are jobs in manufacturing and logistics or most likely the service industry where there needs to be people working every day of the week.
But in my case, which is an office job, the 5 day week is bullshit. Here's how it works at my company: Mondays, Wednesdays and Fridays we have to be at the office. We get 2 days of work from home: Tuesdays and Thursdays.
Me, being the slacker that I am, don't do shit on the homeoffice days. I wake up 3 hours after I'm supposed to, only because I have a daily meeting that I have to attend and everyone must have cameras on for the meeting. Once this meeting is over, I don't do shit for the rest of the day. I mostly watch videos on YouTube or browse Reddit and keep my work phone close in case someone messages me. This way I can reply on time and pretend that I'm doing work.
Despite not doing shit and slacking around for 2 workdays of the week, I am still one of the top performers in my team. That's because when I actually do go into the office, I do work and get things done.
This just serves to show that the 40 hour workweek is simply idiotic for anyone that has an office job. When people are at the office they usually spend 2 or 3 hours doing actual work and the rest of the day pretending to work. In WFH you don't have to pretend.
TLDR: People are way more productive when they work less, everyone sees this, and developed countries (or progressive companies) are starting to adopt the 4 day week.