I don't doubt your observation - I merely point out that you are in a bubble. The vast majority of MBP users I have observed use it open. As you would expect.
For a start you've lost a useful screen. And the thermal performance must be awful.
I have two 27” monitors in my office, and using the MBP’s screen just does not feel useful to me... and yes, I have tried using it on more than one occasion.
I work remote and don’t have an external monitor a lot of time.
When I do my laptop stays open as a secondary screen.
When I’m at HQ most people have the setup above.
My wife has no external monitor. My entire non tech friend group has pros and don’t use them connected to any peripherals.
Primary display is a 27” or 32” 4k monitor w/ standing desks.
Most hate the butterfly keyboard. Lots of mechanical USBs.
Some like the touchbar. Not our blind developer.
I think of them as Mac Minis, before the recent line upgrade.
I see hardly ever see any developer using anything other than macOS (it's not called 'Mac OS'). I don't think the majority are in some niche like marketing or media.