Middle management time breaks down like this:
- 40-60% trying to figure out how to turn large strategic goals into projects digestible by your staff
- 20-30% coordinating up to get permission and sync with senior management, and then coordinate workshare with your peers
- 20-30% coordinating with your staff
- 75% of your time then gets sunk into squishy people problem stuff most people would call "HR problems"
"But this adds up to over 100%!" - yup
When an HR problem arises, at least 8 hours will immediately vaporize out of your schedule. It's not uncommon for bad situations to turn into multiple days to resolve.
On average, in my experience as a manager for the last 20 years, you will lose about 8 hours per month per staff member to "HR problems". It doesn't mean every staff member has these problems, but there will absolutely be those that have multiple repeated issues that take a long time to resolve. If your average work week has about 21 or 22 work days, you've just designed a full-time staff manager who does nothing else. Imagine performance review time in this structure where each review requires this staff manager to solicit performance input from each staff members task manager. I can tell you from personal experience it turns into a solid month of long nights and zero staff satisfied with their review.
This kind of construct does exist in many companies, but most companies have decided that it's more efficient to have the staff manager and the task manager be the same person, even if they have to swallow the fact that it makes organizations less flat as that manager simply doesn't have the time to deal with so many people as direct reports.
And voila, corporate hierarchy.
There are certainly managers who deal with having so many direct reports by simply not allocating time to staff management issues (i.e. HR problems) or not dealing with them in a timely fashion. The result is usually chaos, high-turnover, blah blah, but the actual end result is that staff become fungible units as the organization has to plan around this effective unreliability.
Staff also have fewer career growth options as the divide between worker bees and management transition becomes an insurmountable gulf. New management staff then tend to be brought in from the outside, and don't know the business or products. Enshittification occurs because the only comprehensible strategy anybody can cling to is revenue growth.
Anecdotally, the places I've worked that were flat all featured these characteristics while well balanced hierarchies were able to grow, build long-term strategies, and had high-retention rates.
For the record, I've had as high as 20 direct reports where I was both staff and task manager and it was hell on everybody. I've also had as high as 75 reports in a well structured organization (no more than 5-7 people per manager) and it was totally fine. Companies were software, R&D, or some mix.
Note: the average Googler stays at Google for 1.3 years. In my current company the average employee stays for just under 5.