As much as I agree with that I'm still at a loss as to why butts in seats management is still so dominant today.
Because managers up a level have no other way of knowing if you're being productive or not. So they look and see if people are ferociously typing. This is not a joke.
Yes, a place where I used to work once sent out a memo trying to encourage more regular work hours because management couldn't find people, and the office always looked half empty. The thing is, it was the operations staff for a astronomical observatory. The "missing" people were generally traveling and/or working at night!
I used to work in research physics and recall hearing a similar story, probably embellished with each retelling. The version I heard had the staff complying with the order and working 9-5, then management complains that no observations are being made at night.
Well, in this case, I personally received the memo. Knowing my co-workers, however, I highly doubt anyone actually changed their behaviour due to it. Other, similar, management antics included scheduling meetings first thing in the morning and complaining that the telescope operators never showed up.
The value they add is easily measurable, but it's still quite difficult to tell whether their performance is due to individual merit or external factors.
For example, in any given year some traders are wildly successful (and reap huge bonuses) but year to year their performance is variable enough to be noise - it's not clear that really good traders really exist. Some are just bound to get lucky.
Similarly sales guys may appear great because their product sells itself, or terrible because of a downturn in the business cycle or sector.
It's not insane to want a read on "how hard are you working" or "how skilled are you" that is independent of all the messy confounding variables of the market.
Because managers up a level have no other way of knowing if you're being productive or not. So they look and see if people are ferociously typing. This is not a joke.