Employees (middle management and down) are explicitly structured to use salaries (to reduce costs/earnings from going to them).

Salary is generally a flat monetary incentive, and bonuses aren't big enough typically. You make more money by promotion up a rigid hierarchy: so that is the true motivation.

And that is politics.

If you have salaries, you have politics, and a downward trend towards more of them.

Engineering workers are often idealistic, which is a different set of motivations to exploit by management for monetary advantage. But idealism/creation leads to turf wars and emotional investment in "your code", which is another entire axis of politics.