The problem with academia is basic mathematics. In a system where there are a fixed number of tenured professorships, where each tenured professor has the job for life, each professor should produce only a single tenure-track PhD student in their entire career.
OK, so to deal with attrition and other unforeseen circumstances, perhaps 10 tenured professors should produce 11 tenure-track PhD students. But definitely not the situation we have now, where each professor produces dozens of PhD students in the course of their career who go on to attempt to get tenure.
The people trying to get tenure don't want to admit the system is broken, because that would be to admit they just weren't good enough to get tenure.
The people who have tenure have every incentive to keep it going, because it means they have an army of highly-skilled and highly-motivated postdocs willing to work long hours for peanuts for a decade or two.