I can only speak from an engineering/tech perspective as that's the only field I have worked in. I have worked a total of about 2.5 years, for some very big name companies, as well as a startup, and know a lot of people working for Google, Microsoft, Facebook, and a gazillion startups, etc.
Both from my personal experience and experiences relayed by friends, ALL of the most effective managers have very high technical backgrounds, and most of them do not have management degrees.
Like cambio wechsel said with the swimming analogy - you have to learn management by doing it, and to get there, you need to be better than everyone you manage at what they do. A management degree doesn't really prepare you for that.
To be a manager at a software company, you need to be a very good software developer yourself. To be a manager at a pharmacy, you need to be a very good pharmacist yourself. To be a manager at a car dealership, you need to be more knowledgeable about cars than all the sales people.
You can't just get a management degree, and walk into fields that you have no idea about, and expect people to hire you to lead their teams. It just doesn't work that way.
One use I can think of for a management degree is if you have a degree in something else, and worked in that field until you become a manager, then do a management degree so you can do your job more effectively. Even then the value of such a degree is debatable (I personally believe it would be somewhat useful).
I also don't have as much respect for business degrees as I do for most other degrees, because I don't think they are really "creating" any value for humanity.
If you are a doctor, you are helping people staying healthy and regaining health. If you are a scientist, you are discovering aspects of the physical world that were not previously known, and can potentially make the world a better place. If you are a psychiatrist, you are helping people becoming happier and helping them combat mental illnesses. If you are an engineer, you are pushing the human frontier of technology and solving problems in the world. If you are an architect, you are building bridges and houses, which obviously benefit humanity.
If you are a business person... you are shuffling money around, making some people richer and some people poorer, without really adding any net value into humanity.
I think similarly of lawyers.
And I don't think I'm alone. I believe that's why a lot of people don't have a lot of respect for business people and lawyers, not just because they are usually rich. Doctors and engineers are usually rich, too, and they don't get nearly as much hate.
Yes, job prospects are good and you can probably become very rich, but when you die, what will people remember you for? If you are an engineer, you can say you built bridges. If you are a doctor, you can say you saved x number of people and performed some very difficult surgeries. What about you?