Managers are also like movie directors. I’ve been on projects where smart people can focus on the wrong parts of a project. Sometimes it takes one person to orchestrate the band, hone in one what is the true impactful work. Shepard the sheep through to the finish line, especially if they are headed in an ambiguous direction.

Now, what’s all that got to do with having butts in a seat that you can physically see? Jack shit really.

I think what you are talking about with the former and technical leads and product owners, not typical people managers. There is overlap, as it gets fuzzy, but most managers I've experienced have terrible technical insights and are instead an active blocker to great results.