This is the key thing here - Uber for instance doesn't need to solve L5 self driving. They need to figure out what routes are frequent in their network and what routes can be driven by their self driving car and route a ride appropriately.

It will never be Uber flicked a switch and replaced all their human drivers. It will be a very gradual transition over to self driving that may never reach more than 25-30% of all trips.

Is that worth the billions of dollars they're pouring into self driving? https://www.uber.com/newsroom/company-info/ says they complete 14 million trips a day. That is 5.1 billion trips a year (and growing). 10% of that is a 500 million trips a year. Assuming the average trip is 13$, that would be $6.5 billion per year in revenue, I think that's more than enough to turn a significant profit even accounting for R&D, Capital expenses to maintain the fleet etc.

The reason self driving will be a reality is purely economic. Noone's developing it to change the world or reduce the number of people dying in accidents or whatever shpiel they cook up.