A percentage > 90% of the world isn't programmers...
There simply isn't the same workflow to monitor "word" / "pdf" documents without an insane amount of effort / document control that most SMB's dont have.
The only option available to them, without hiring programmers, is often only the metrics that get offered built into these types of products.
I dont think that's a strawman argument.
Most trivial things can be measured outside time. Many jobs measured on time, we already know why they are measured on time (low activity, presence-based jobs). Anything else, measuring based on behavior/time spent is management being lazy and not doing what they should be doing: comparing inputs and outputs, and measuring the impact of changes to them to improve productivity.
If a manager can't do something that basic, they shouldn't be looking for more bad proxies to hound people with. They should be doing the company a favor and quit.