Well if there's profit to be extracted it's a sure bet deep pockets will extract it so I can only see it going this way:

1. Private equity and major corporations create robotaxi fleets
2. They all compete - some go out of business, others merge
3. It settles into an equilibrium where each city is a duopoly, giving the appearance of competition
4. In reality though the prices are artificially high because as the price point they stopped competing at includes large profit amounts.