It's all about network effects
"The ability to keep operating in these legal gray areas is integral to the value propositions these companies are making to Wall Street. If we started using old-school interpretations of antitrust law, forced companies like Uber to follow labor law, or treated Facebook like a public utility, these companies wouldn't go away. But they would become much more modest — the massive payouts investors are expecting would never come, and the companies' stock valuation would plummet.
This gets us back to the IPOs themselves. When we say Uber is worth $100 billion, for instance, there's no actual pile of $100 billion sitting around that Uber's owners can draw on. It's all conceptual value. And if Uber's play for maximum network effects fails, or the government actually starts regulating it, that conceptual $100 billion goes away."