Specifically, let's talk about "cost." I did a biology PhD at a respected school in a low COL area. The annual stipend, when I graduated in 2019, was around $31k. It was enough to afford basic necessities (rent, food, car) with a few hundred dollars to spare. Obviously, not enough to start a family, but I wasn't subsisting on ramen noodles either. Plus, the work I did as a researcher is something I can put on my resume as actual work experience.
Stories like the above, about people going into massive debt for graduate degrees, send chills down my spine. I can't imagine the cost/benefit calculus that steers people onto that path.