Managers have a ton of pressure on them to perform. But part of their role seems to be "just one more thing". They face a barrage of requests from various people to perform additional tasks. They are pretty much run ragged. There is only so much you can do in a day so something has to give. The number 1 candidate for being pushed aside in favour of that shiny new idea is team development, usually coaching.

This podcast explains why that isn't a good idea.