That's because many engineers 40+ have at some point during their stint as an employee looked up from the code editor and understood how business works, realized there is much more money to be made running your own consulting company instead of competing with 25 year old leetcode whippersnappers for a lower salary and manager/PM abuse, stress and rejection after rejection as you try to get your next gig every few years, maybe after a layoff etc.

After all all those layers above the software engineers, i.e. the coal miners actually getting the coal out of the dirt, (mangers, product owners, CTOs, CEOs and so on), essentially get paid from the work of the software engineer in a profitable company, when you get business savvy as a software engineer you can cut all of them out by starting your own business.

In short, you don't see them because they're not employees anymore, they're business owners.