Maybe driving a Uber in Washington DC lets you meet some interesting/useful people?

Plenty of Uber drivers only drive customers when they're already heading from one place to another. Since you pick what fares you want to take, a professional leaving from Fairfax to, say, NW DC can exclusively accept a fare going from their relative location to their relative destination.

This wastes maybe a couple of minutes. But it does provide company and perhaps an added member to your network, all while earning you (perhaps negligible amounts of...) money. All this to say, maybe they can run a startup and drive Uber.

Food on the table until investors found?

I would also guess it's a networking strategy.