Because management can't manage.
We are engineers. So we think in terms of what you'd need to do, to achieve effectively statistical certainty that you'll be able to send a plane on it's way in almost all cases, while minimizing costs.
Such a process would involve a set of actions that you'd have to execute, as a management team, using a set of employees, so that everyone is in the correct place at the correct time, and the odds of anyone getting into trouble is minimal, and this gets planned out over time, optimized by a scheduling algorithm.
Then, if things go wrong, you simply re-run your algorithm to deal with the new situation and you do the best that can possibly be done. Of course, such a program is very hard to write.
The stories I've heard about management actually doing this are VERY few and VERY far between, and even then only about very specific things (and only things that would apply to multiple airlines, e.g. optimizing flight plans and fuel tanking). Instead, management layers simply threaten the layer below them into perfect attendance (which works for a while when employees are desperate for jobs) and when things inevitably go wrong they go into full panic mode and spend 50x what is really necessary to fix things. During such panics, even basic events seem to come as total surprises to management. For instance, there was a news message about a problem in Amsterdam Schiphol due to the weather. The problem was understandable, a re-frozen ice layer on the tarmac prevented safely taking off. 10 or so flights got canceled for one airline, for close to 2000 passengers, and there were 2 customer service representatives that, obviously, had a rather hard time dealing with this (there were 20+ doing ticketing for flights that weren't going to happen ... but using those ... nope). Management eventually provided hotel rooms for about 800 of those passengers and put beds in a terminal at around 6am for the rest. Lots of court cases are underway, and are unlikely to go well for the airline).