>The platform puts most of the financial risk on the labor side (drivers owning the cars if you're driving Uber, owning the house if you're Airbnb'ing it, etc.)

Actually people already owned the cars and already owned their houses. How is that a financial risk? These platforms allow people to use their existing resources to make money. That's efficiency gains.

If anyone decides to acquire new vehicles or properties to use on these platforms it's because it's profitable due to the large demand driven by these companies pouring billions into customer acquisition and customer relations/support for them.