Do PhD students have much choice which supervisor they can choose? Supervisors do not come in all sizes, most of the time you have to deal with whoever is out there, whether you like them or not.

I have worked within academics, not as a researcher though, and from my experience academia is not about pursuing the knowledge and sciences. That's an intrinsic motivation some researchers still might have. Academia is rather pursuing prestige, which comes from successful researchers who are guaranteed to attract grant money for projects. And this is computer science alone. Most post-docs just don't care, they are doing everything as if it's their hobby, not work. Those who care do not last long in their field. Also, students are the hardest working bunch in academia, and are paid the least. Sure, when a student is failing, it's their own fault. No one has ever fired a PI, because their student failed, why or how doesn't really matter, right?