Except for meetings and deadlines, why is anything measured in hours. Why aren't things measured in amount produced? (I hope it's obvious I'm speaking in terms of coders and manager's teams - I have no idea how this would work for directors or above.) The majority of coders are employed on salary (so far as I know), so just pay their salary and expect tasks to be completed. This mandatory 40 hours in a seat ritualistic adherence seems dated and unproductive. Different people will work better in different situations, and it is one of management's tasks to see that their team's potential isn't impeded when trying to complete their tasks as a unit, even when that means working as a coordinator between separate individuals on the same team, working towards the same goal. The work should be what's valued and not some myopic adherence to a past life of offices and collared shirts.
It's because workers in general don't have much leverage when it comes to being compensated for the value of the fruits of their labor instead of just their time. Owners want to capture that value instead.