It’s not just PhD programs that aren’t worth it any more. Law school applications have plummeted. Full-time MBA’s in the United States are of doubtful value at best, especially when opportunity cost is considered. Even medical degrees are now a huge financial risk.
Instead of going to graduate school, students would be better advised to do more with their undergraduate degrees. The value of studying math is difficult to overstate. From engineering to biomedicine to insurance and finance, understanding calculus and advanced statistics opens doors. This is true regardless of whether a BA is useful mostly for human capital development or for signaling (math is hard for most people). I recommend a minor in math to most undergraduates. Alternatively, computer programming and web development can be self-taught — you don’t even need to go to college.
The rewards that the Ministry says are there is not the ones you want to think about. As Sorens notes you need to take into account the opportunity costs of getting a degree to judge whether it is worthwhile, and once you do you may well find it isn’t. Also consider life time earnings, not just fives years worth.
Or you could just think of your education as a consumption good rather than an investment good.