It seems to be a global universal, with a few stellar exceptions like Japan, that we suck at developing managers.
There appear to be two primary approaches to manager “development”:
1) Hire MBAs
2) promote and float: throw them into the job and see who survives. Have their equally unskilled boss coach them.
Good organisations have management development programmes at work to grow managers over time. We all know it’s needed but it’s all too rare.