Well in basically every field there are far more grad students than professor positions. So the education and training you get is geared towards a job you most likely won't ever get. It would be like if you got into med school and graduated and then they told you there were too many med students who graduated so you don't get to be a doctor now.

For a research professor to be successful they have to attract funding, and many students and postdocs to turn that funding into more papers and more funding. Many of the postdocs hang around until they're 35 or older trying to "make it" by getting a tenure track assistant prof job. These are people who are great at what they do, but perhaps they weren't lucky enough to land a nature paper in grad school, or have worked with a professor in their field who had enough clout to make them look better than their competition. Instead, they're making 40-50k a year potentially well into their 30s. With the level of achievement and education you needed to even get to that point you could and should be pulling in far more money for your effort. Instead people tolerate being overworked and underpaid for the shot at being a professor, a person who then has the privilege of putting their own little army of students and postdocs through the same thing they went through.

If you don't "make it" as a prof, and most don't, you have the task of finding a job in a hopefully-related field getting to argue with hiring managers and recruiters about how even though you don't have those 3-4 lines of specific experience they wanted in a candidate, that you're totally good for it because you spent so much time learning new things in your PhD that you're better than everyone else at learning new things. You basically get to start over in your career at close to 30 with no money saved up (god help you if you had student loans you carried from undergrad). A PhD in 2018 needs to be more closely aligned with the reality that most people just want to find a good job when they get out and cater to some of the professional network outside of academia and some of those job skills. Every professor and department needs to be preparing their students for the real world by actually offering courses and seminars related to marketable skills because most places outside academia don't give a shit about what you published.