To me, one of the most important factors that differentiates a good PhD program in the US and a bad one is the teaching expectations placed on the student. In some departments, PhD students are expected to be instructors of record without any TAs assisting them for 2 sections every semester throughout their entire program, whereas others have literally no instructor requirements. This makes a huge difference in how much time a student has to work on getting publications and conference presentations and finishing their degree in a timely manner, which then makes a huge difference in their prospects for landing research posts in academia.

However, I know of large programs and very small programs that manage to have very little if any instructor requirements for their PhD students. The size of the program doesn't appear to be a good predictor. My assumption is that it more comes down to how much money a department pulls in through external research grants relative to the number of students they have so that if faculty are not getting grants and hiring students as RAs, the burden is 100% put on limited internal funding, which means they need students to shoulder more work than they otherwise would have to.

Is this generally the case or is there some other major factor that creates this situation? My only other thought is that the way the university is organized or the dedication the state has to the university could make a big difference.