One of the other reasons is that training tends to be bad. We actually train people to be managers — train conductors and spreadsheet jockeys — instead of training them to be leaders. Fundamental flaw but “That’s how we’ve always done it!”
The biggest gap in middle management is leadership training, the ability to focus on a 3-5 year vision for the team instead of focusing on the challenges immediately in front of you and your team.
Without leadership at the middle manager level, teams have difficulty connecting the company vision and purpose to their area of the business, how they go about doing their work, identify skills that need to be developed, roles that need to be created, structures, processes, and technologies that need to be put in place.
Teams become stuck in a never ending stream of fire drills, constantly reacting to short-term changes without understanding what they are trying to create. The know where the company is going but not their team and it makes rowing the boat significantly harder.
When it comes to the direction the company is heading, the people in middle management tend to believe that the C-Suite or product area GM's are solely responsible for setting vision and leading the company or product area.
The truth is that everyone in an organization can create a compelling vision that is inspiring, clear, and practical. The trick is making sure that the vision you create is scoped to your area of ownership and is aligned up and down the different levels of the business. The same goes for strategy and how you and your team work... this is how organizational create leverage at any scale.