The longer students stay in a PhD program, the less likely they want to be professors. Typically many first year students say this, but the numbers quickly drop off in later years. When I was a PhD student, I gave a few talks and blogged about this issue. I would present all these statistics in my talks about what they needed to do to be competitive, and people just absolutely hated me for it. One person said she wan…
I think that also goes to answer the question about motivation despite long hours and low salaries. Knowledge is its own reward, I guess.
Also, doing work that really satisfies you is a big privilege. Big big privilege. Not many people enjoy that, the world over.