[nostrademons]

Because that's the incentive that management faces. Their promotion is dependent upon having more headcount under them. The key metric in their resume that determines which jobs they are qualified for is how many people did they manage. They don't personally pay for that headcount. If they meet some baseline of output people don't really ask questions (or are able to judge) whether that headcount was necessary. So of course they seek more headcount.

I suspect the economy would look very different if total headcount in a manager's org was the denominator in a manager's performance review, such that if you employ 10x as many people, you better have generated 10x as much profit. But this would also have lots of unintended consequences: management would be incentivized to employ as few people as possible, which means lots of people would be out of work and would be competing with your firm.