That is exactly why a lot of academics chose the academic career in the first place. There was a lot more freedom to pick your own problem and work on it than you'd enjoy in the average corporate job. There still is, for the most part. But if that advantage is eroding, it's worth talking about.
If you looked at the numbers and decided to try it anyway, you only have yourself to blame if you fail after throwing away years of your life. You didn't blaze a path, you didn't do things substantially different than your forebears.
If you naively didn't look at the numbers and kept going out of blind faith, then sorry, you wasted your twenties and got only hard experience to show for it. Don't feel too bad, 90% of your academic peers are doing the same thing. I wasted my twenties too doing stupid things. Probably most of us did. Just don't pass your thirties the same way and you should be fine.
A pyramid scheme works well when the pyramid is expanding. It doesn't work so well when the tip of the pyramid is shrinking.
If EACH tenured professor has 1 graduate student per 3-5 years, that's nowhere close to the rate at which new tenure track jobs open up. There are some private sector jobs for Math PhDs, but even those have an oversupply.