I have worked at multiple tech companies, and I still don't understand why an engineering manager is not a manager for one area of the product. The manager's re

I have worked at multiple tech companies, and I still don't understand why an engineering manager is not a manager for one area of the product. The manager's reports should work on a specific, well-defined project together, and the manager should be guiding that project to completion. When it's done, move on to the next one on the priority list. Everyone on the team would be a "product manager" because they should all be involved in understanding the value of what they're building and what customers think of it. Instead we have a strange overlap of HR, engineering manager, technical program manager, project manager, product manager, tech lead, and tech lead manager. It's unnecessary.