There is no any such reason.
Current day managerial jobs descend directly from days of feudalism and aristocracy. Where the master had to be richer than the slaves to enforce his rule over the serfs.
All the best having a underpaid manager exercising control over overpaid ICs, it doesn't start, let alone work well. In short this is social sanction.
The reality is any set up which require a pyramid to exist, there will be pay grades, people down the pyramids will be paid no matter what miracles they will pull off. And people at the top will maintain political control to further their interests.
That is all there is to it. If we evaluated these 'managers' on merit. Then even being called a supervisor would be a lot for these glorified email routers and table fillers.