How many businesses are there that are worth at least $1 billion and employ no-one but the founders?
When people say that it's not possible to earn a billion dollars, they're talking about the discrepancy between the wealth gained by those employed by the company versus the shareholders of the company. For example, when WhatsApp was sold to Meta for $19 billion, how many of WhatsApp's 55 employees walked away with hundreds of millions of dollars?
The fundamental problem is that it's possible for an employee to generate a hundreds of millions of value for a business, and yet be compensated for a vanishingly small fraction of that. Even if the employees agreed to a particular salary, is it ethical to pay them so little in comparison to the worth they generate, or is it exploitative?
Most, if not all billionaires, reach that status by paying people far less than the value they generate. If you want to become a billionaire, you need to find people who are willing to be paid thousands or tens of thousands of times less than they're worth. You need employees who will generate you $100 million in exchange for being given $100 thousand.
This wouldn't happen if employees rejected cash-based compensation and decided to be founders themselves. Most employees trade risk for higher cash comp, and end up with less upside. This issue is mostly settled by the employment market
Your post implies that every employee of a successful company is entitled to a share of whatever wealth that company generates.
As a career programmer, I worked for several companies. Each time I took a job, I negotiated what I thought was a fair salary for my wages. Some companies also gave me stock options and one gave me founder's stock. When a company had a good year, they often gave generous bonuses.
Only when I took great personal risk, did I expect to share the rewards that come with a successful company. I was always grateful when I got more than I agreed to work for, but I never felt entitled to it.
A janitor working for a 10x company should not feel entitled to 10x of the salary as another janitor working down the street for another company that is struggling.