I think the biggest issue is the IT culture in general. I come from a military background, and there was tremendous emphasis on developing your subordinates for 3 reasons:

1. You knew many of them would be in the military with you for many years to come. Even if they were not with you in that assignment for long you would likely encounter them again, so their ability to do their job would impact you for a long time to come.

2. Developing your subordinates was a major part of your evaluation because the military assumed that it would have that soldier for years if not decades.

3. You knew their performance could directly affect whether you came back in one piece.

But in most civilian jobs none of those are true. Especially in the ecosystem where I work in IT, it is very common for good employees to leave after one or two years, this makes the ROI for training much lower from the corporate standpoint and the standpoint of the individual manager. If employees could be expected to stay longer the company would see more benefit in developing individual employees rather than just replacing them with someone else who already had the experience. If the company emphasized that and it impacted IT managers salaries/bonuses/promotion potential then you would see a lot more managers paying attention to development.

As it is now, a smart person in the IT field would learn to learn on their own regardless of how much or how little management support there was for it.