Because self driving cars would allow people who otherwise couldn’t drive for themselves to own yet another car on the road. Teenagers, elderly, people with chronic alcohol addiction, you get the idea.
I don’t fully buy the “no traffic jams or accidents” thing either. There is definitely the potential for there to be less, but what you are talking about is something that isn’t going to happen for ateast another decade. Surely you remember the Tesla crisis from the last year?
I can see ride sharing becoming a thing for the people under the poverty line, but realistically speaking, everyone is going to buy a car. There is no incentive for a billions of dollars company to put less cars on the road using ride sharing, some of them already sell you heated seats in the form of a monthly subscription.