I manage a team of 21 developers,
All that and you still can't help bragging about how many people you've managed.
Clearly, you have never worked for a good manager. I'm sorry for you. Good managers do exist. As a manager myself
That's why you're not climbing the corporate ladder. Get more people under you ASAP. Learn to fight off your rivals. Or stay down.
I suspect is from sheer ignorance rather than any design to get more workers underneath them.
Wrong. Managers are always scheming to get as many people below them as possible. Claiming savings is an effective short-term strategy that only works in specific circumstances, and it only works as a strategy when it results in more people below you on the org tree.
The rule on staying alive as a program manager is to give 'em a number or give 'em a date, but never give 'em both at once.