Who can bootstrap a business like this? So people are staying with their powerful big corporations if they can't get millions in funding for a startup (and outside of tech this is simply not even a consideration).
Edit: and if at some point you hire an employee, you will need / want to provide them with health insurance, and it will cost just as much. Large corporations have an advantage in that they negotiate lower premiums in bulk. Add this as yet another barrier to entry, along with their lobbying for protectionism, tax loopholes, their ability to hire huge teams of tax lawyers and accountants, and if you really start to get their attention, they can sue you baselessly by throwing lawyers at you to keep you in court. Merely defending yourself and getting to the point of dismissal is unaffordable for a budding small business.
Take a look at S&P500's profit margins. They are at record highs and not coming down as economics teaches us, meaning new entrants are not coming into the market.