The same reason you don't put a space heater and window AC in every room. Because it's inefficient, ineffective, and archaic.

Yep, you want the whole thing to act like a system not a bunch of parts. Energy savings and a comfortable environment really depends on this. A poorly setup system can be a nightmare for the maintenance staff.

And so this is why, in our office with a thermostat and ducts in every room, it's typically freezing in 1/3rd of the conference rooms, another 1/3 are way too hot, and there is zero meaningful control using the thermostats in the rooms over this?

Not saying it's not a good idea, just saying that in reality I've seen these systems work very poorly together in most office environments I've been in.

Well, if you have thermostats in every room, I would imagine that it would be impossible to get a consistent temperature. All the commands and one system to sort it out and move air cannot be good.

If I ever teach a CompSci again, I would think about making a climate controller a problem set. My first choice is a storage building controller, but this would be interesting.

That sounds like bad air balancing, but that the control system is "working".

A big reason is cost-savings. This prevents each building occupant from setting the AC too cold, or forgetting to turn it up/off when they leave at the end of the day and for breaks.

The best way to set the temperature at a comfortable level is guessing every 30 years what you want each building to feel like.

Do you expect that over the next 30 years our idea of what a comfortable temperature is will change?

Temperatures are set based off things like use of the room and season. Both of these change and usually only one is somewhat predictable.

Are we sure that the current system doesn't have that?

Even if they do install local controls, a central monitoring system makes some sense for buildings that go unoccupied for days at a time.