Because most of us are middle aged with mortgages, kids etc. Not old enough to retire and live off of savings or 401ks, not young enough to start all over again.
Starting over isn't worth it anyway. Entry level is being hosed the worst, so this isn't an issue you can retrain yourself out of.
I was offered an MBA for relatively cheap, but the sort of PM/Middle Management roles that most easily opens up are also feeling pressured by AI Layoffs and seeming to disappear from the job market. Even "relatively cheap MBA" doesn't at the moment look worth the opportunity cost.
Of the suggestions from friends and acquaintances, the one that would have sounded bizarre to me four years ago that somehow sounds like one of the most viable suggestions I've heard is applying to Law School and getting a JD. That doesn't sound like a great use of my time either, and I do still have a mortgage to pay (even if no kids to worry about) if I did go back to school, but suddenly in this economy it sounds like one of the more useful suggestions I've heard in recent months since my last layoff.