That is not necessarily true and simply a choice individuals make. The more you make the more you can save. Most degrees have lifetime earnings supplement of over $100000
after expenses. You can choose to spend or save that. Its not much but it does get you there sooner. I have lived it, I don't need a book to tell me my life's story.
I totally used to believe your point of view.
When I started actually seeing those fancy MBAs in their BMWs and Italian suits, I saw that the vast majority of these high earners actually spent more than they made. They had more credit card offers with higher limits and almost all of these people had debt and if they had any cash in the bank, it was only for nice toys (adult toys) or vacations.
I look back before college and when I spent my late teens and most of my 20s as a blue collar guy and there were plenty of very frugal peers I knew who invested wisely and widely and played a long term game plan for success. They lived within their means and had their own small businesses. It was a mindset the blue collar people here had. The most extreme success story was a grocery store clerk who stayed at his mediocre job and bought fixer uppers in bad areas. In time he eventually had ten houses that he got working (at least into a state of working legally

, not mansions mind you) and by age 55 he was financially independent. Since this is silicon valley, you may need about $3 million in cash/houses paid for to be truly independent where you don't have to work anymore, or neither do your descendents.
One lady I know had the high profile high tech job here, had to keep up with the Jonses to help make San Jose a destination for the new rich and she ended up with $300K life savings (cash) at the end of her life. She could have had more but the nice clothes and frequent car changes go with the territory in big cities with high salaries. There was no way she was going to be independently wealthy here so she moved to rural Maine where she bought a giant house for $36K cash, got a rugged used vehicle, and is now financially independent. Her path was moving to an area where $300K was what Bob Brinker would call financial critical mass. It's different for all areas so a mere millionaire with one million may or may not be financially independent.
Also look back at the post that talks about professional sports players who made a lot but usually ended up broke or in debt.
Again, it's not what you make, it's what you save vs. your current income. And with what you save, long term, it's investing wisely and diversifying and avoiding get rich quick schemes. College has little or no relationship to this. With 30 years in the working field, the ones I have seen really make it big were not those MBAs, but regular humble working people who lived simply, save, and invested.
But yes, there is the occasional plumber or construction worker who saved and played the money game well and decided, at age 40, to get his college degree and MBA, just for kicks. Many of those people fall into your statistic of rich and educated. Adult learners, many of them already set up financially, are fast becoming the norm and not the exception. To add to that, I have never met anybody more interested in every aspect of going to class as that older person who went for their education for the joy of learning.
They are the ones who got the As in every class. They are the ones who often know more than the professors. For this purpose alone, I wish all could go to college and get their associate's, bachelor's, or graduate education.
Online learning has really made this an accessible possibility.