Many people place a special value on “doing what you love”. Should you become a corporate tool, or a real-life scientist? “You should do what you love” is the reply. And it’s a reply that is detached from any real cost-benefit analysis. Like, maybe you only sorta love being a real scientist, and maybe you don’t love the working conditions of a scientist, and maybe the salary of a corporate tool is so much higher that it enables you to do other things that you love. But you can’t make a snappy motto out of such considerations.
The problem with “doing what you love” is that it doesn’t come for free. If academic institutions need a certain number of grad students,* then they need to provide incentives for just enough people to apply. “Doing what you love” is one incentive, and it takes the place of other incentives that academic institutions could have offered instead. In other words, they don’t need to pay you well, or treat you well. However much grad students are willing to tolerate in order to do what they love–that’s how much they end up having to tolerate.
*I’m only talking about Ph.D. students and not Masters students. I’ve never heard anyone describe a Masters degree as doing what you love.
In economic terms, we can speak of the “marginal” grad student (a concept similar to the “swing voter”). For the marginal grad student, the expected costs and benefits are exactly equal, such that the decision to go to grad school could go either way. It may be that the marginal grad student thinks they would love being a scientist, but this is exactly offset by the costs. So for some people, grad school may be a good deal. But the deciding factor is not merely whether you love grad school, it’s whether you’d love it more than the marginal grad student.
Beyond that, I think even the marginal grad student is getting a bad deal. The marginal grad student expects they would love grad school, but ends up loving it less than they predicted.