I'm a PM and I work from home - far and away the biggest advantage IMHO isn't the lack of commute (though that's great), but rather the flexibility in schedule.
My most productive hours are 6-9am - I can crank through what would take me most of 9am-5pm in that time period. That's wasted when I have to get ready and commute during that time period. When optimizing for most efficient working times, 40 hours a week is really 20-30 depending on meetings.
What are you accomplishing daily at 6-9 am when most people aren't logged in? I know there's like a lot of individual work but when do you work with other people? Do you just work less efficiently during the day you mean?
* I can sustain hard mental labor (including but not limited to work) for about 50 hours per week total
* I don't know when I'm going to be in the best state to do that work, and it depends on a lot of factors
* Some of those factors are external, some depend on the project, etc.
* Sometimes, that mental labor needs to go somewhere else, and that subtracts from my overall work budget. That includes things like weird social situations, fixing something around the house, etc.
* I also spend a lot of time passively daydreaming about the last thing I worked on. This is often productive, but also often isn't.
* My productive output also varies a lot on those factors: some weeks, I can produce 60 hours of work, and others only 15-20
I think if you have bursty work patterns like this, it is actually beneficial to have more office days rather than fewer, to "catch" as much productive time and daydreaming time as possible. However, it's an even better argument for remote work, because that minimizes other forms of mental labor, like driving.
The whole idiocy around 5 days a week 9-5 is because people think you have to be in office all that time. People can and do take random half days, hours off to go to the dentist or the doctor or to the post office or whatever the fuck. That's how it has always been. There are very few jobs that require you to literally never fuck off if there's nothing going on. Work adjusts around you if you're a productive person. Some of us can get stuck with shitty bosses and everyone empathizes with that, but for the vast majority of folks, the boss absolutely does not give a flying fuck about when you come in as long as he knows you're disciplined.