I had the same question while reading. It's probably obvious to the startup crowd, which is why it wasn't made explicit, but I think the trick is this: a company which will never make a profit is (should be) worth zero, but a company that has the ability to make a profit in the future is valuable, even if current profits are zero. So rather than making a profit and paying it to yourself, it's better to make the company as valuable as possible to other people by reinvesting everything, and then sell stock or borrow against it for your own consumption. That definitely seems true for the most prominent outliers, but no idea whether it's actually true for the average or median owner / founder.

I guess this why EBITDA is important: if you have positive EBITDA and stop growing the business, you can pay off your loans, finish depreciating your existing equipment, and with I=D=0 you have real profits.