Those two effects are mutually opposing forces - are car owners willing to take the risk of someone contaminating their car by smoking, spilling, eating, puking or having sex to earn a pretty penny?
People who hire robotaxis might need to have money in escrow if they don't have enough reputation.
If you try to rent a car without a credit card, you are usually required to put down a deposit.
Renting a car requires one, but there's also more generally a high barrier to renting a car - plenty of forms, showing your license, booking in advance, etc etc. There's also no choice. The same is not true for getting in a taxi. Why would I put down a deposit to ride in an automated car, really?
Lol