[ModernMech]

> If the advisor's getting cheap or free grunt work

This is a huge misconception. Yes, as a grad student you aren’t paid well. That doesn’t mean you are cheap for a PI. They have to pay your tuition, as well as university overhead related to your stipend. You don’t see a lot of that money in your bank account, but it is leaving the PI’s research grant nonetheless.

The most productive students are those who are about 3 years in when they are done with classes. The least productive ones are those about to graduate; they typically have a serious case of “senioritis”, and are often busy making contacts in industry and planning a career. Keeping them around makes them less productive, not more.

Professors want to graduate them to free up resources and to bolster their promotion portfolio.