Maybe the reason an alternative didn't exist because others realized it was against a lot of laws, regulations and tax codes?

For example, I could start a service that allows people to make food in their house and sell it online. The reality is that in most municipalities you cannot simply cook food in your kitchen and sell it.

The difficult part in Airbnb, Uber and my imaginary sharing economy food service is managing to get big enough before authorities catch on. And getting big fast just happens to be something the VC model is very good at.

In my opinion it's more an innovation of hyper growth VC funding as a means to out run authorities enforcing regulations, laws and tax codes as opposed to the innovation of something built into the individual service of Airbnb, Uber etc.