Why we don't take our Uber driver's phone number to skip Uber fee?

We could take the phone number of Uber drivers and skip Uber fee.
We could skip Amazon marketplace fee and deal directly with the marketplace vendor.
We could skip AirBnB and skip AirBnB fee.
We don't.
Because we like to be reassured by an intermediate guaranteeing a good trade.
Indeed, they do this trade at scale and in a very packaged way.  We feel good using them.
We like smooth experiences and avoiding risks.
Trading is a risk.
I'm not sure humans like risks, and thus, I'm not sure they like trading.
We did that before the internet. We had no choice. Now we have.