When asked what they would do if given a job offer from AMD, Intel, or some other company for a fulltime position with a salary around $60-80k/year, they remarked that they couldn't possibly take those jobs because they'd be "soul-crushing." They pointed out that graduate students in the sciences earn a median of $25k per year, and professors can make even more.

My question is this: how can one rationalize spending 4-6 years and $100-300K in tuition merely to spend 3-5 years on a PhD while making little more than $100k over the entire degree, rather than taking a job offer that could wipe out their student loans in 2-5 years?

Is it simply that the students most optimistic about grad school are the most likely to receive high-paying or high-quality degrees or professorships?