> If an employee generated no additional income to it's employer, there would be no reason to hire him in the first place.

The thing to remember here is that hiring managers aren't spending their own money. And most managers I know (though notably not the best ones) have always wanted to manage bigger teams, both for simple ego reasons and because it tends to lead to promotions and higher compensation (in one company where I worked briefly, title and compensation were directly linked to number of employees managed).

This motivation leads to all sorts of decisions that are suboptimal from an economic perspective, including lots of "bullshit acquisitions".