A couple reasons I would guess:
1. Full carrying cost of an employee is much more then their salary so this math is not as straight forward if you’re just cutting time and salary to account for that time.
2. You should assume most people aren’t counting hours in places like Meta, reducing to a 4 day week imho will start making people think more about counting exact hours they’re working. It’s partially why the “4 10s” concept is also a bad idea that permeates the defense contractors.
3. Staying focused 5 days a week for one person probably has better compounding effects for that week than a few people working part time and taking longer to get the work done with longer breaks in between “sessions”. Harder to measure of course but it’s one thing I’d be worried about. Easier to think about if you say each person works 2.5 days a week for half their pay, I’d rather just have one person.
4. Layoffs let you cut by performance.
Your points seem focused on the bottom line and short term extraction of labor from employees, versus actually building a long-term community of healthy, productive people.
Like this:
> will start making people think more about counting exact hours they’re working. It’s partially why the “4 10s” concept is also a bad idea that permeates the defense contractors.
Maybe that's a good thing? [1]
I have no doubt that Meta is thinking like your four points and hiding behind "it's the corporation making the decisions, not a bunch of people at high levels", but... Ugh.
[1] Nitpick - I was speaking to a friend about a decade ago regarding their OT/IOT work in the defense industry, and they told me that they had to aggressively track every hour. The feds were punitive when it came to unreported overtime.
> the “4 10s” concept is also a bad idea that permeates the defense contractors.
If you're doing work on a cost-plus-fixed-fee contract (which many software development efforts are) then you have to count hours anyway because the incentives are such that your billable time is your product, not what you're actually building. The fact that nothing substantial gets done in the additional 1-2 hours a day is immaterial because these arrangements are really just fringe benefits in the form of additional time off for employees. As a practical example: people working "9 hour days" with mid-afternoon on-site customer meetings and a half Friday from home certainly aren't fitting 40 hours of productivity into their week and nobody cares - everybody gets paid, the job gets "done" (for some value thereof), and millions of Americans stay employed.