As someone who graduated with a 7.5 year long PhD last month,

I feel like PhD stipends are not a major problem. Like I got $40K in a low CoL area, but accounting for tuition and overheads I cost my advisor closer to $150K/year.

Now why are tuition and overheads that high is a reasonable question and it ties into inefficiencies in broader American administrative processes, but I cost society and taxpayers $150K/year, and that I'm doing it for societal benefit is honestly only partly true. The first 6 years was just me building real skills and letting myself be frustrated, and maybe in the last 1.5 years I did things that justify the $1M bill and more.

Even if I did eventually do things that justified the $1M bill, I think most students don't. The larger value IMO lies in a workforce trained in the failures and frustrations of grad school. While I could rattle of plenty of limitations of academia/grad school, I'm not entirely convinced that me being shortchanged/underpaid was one of those things.