If owning the fleet was valuable, there's not much (probably just labor law and some issues with the mythos) stopping Uber et al from owning the vehicles the drivers drive.
I think self-driving is the cold fusion of the 21st century, but the reason unlicensed taxi companies are pursuing it is because if, by some miracle, it comes to fruition, it might make their business viable, but it would be hard to compete with an automaker running autonomous taxis when you have to buy your autonomous taxis from the automaker you're competing with. If they can build it on top of existing cars, it makes it more possible to compete; and if they end up with an enabling patent, it means they'll probably survive in some form.
I think self-driving is the cold fusion of the 21st century, but the reason unlicensed taxi companies are pursuing it is because if, by some miracle, it comes to fruition, it might make their business viable, but it would be hard to compete with an automaker running autonomous taxis when you have to buy your autonomous taxis from the automaker you're competing with. If they can build it on top of existing cars, it makes it more possible to compete; and if they end up with an enabling patent, it means they'll probably survive in some form.