The car as a service option won't be the solution for most families, because they have a lot of nonhuman cargo they need to store in their car: strollers, diaper bags, sporting equipment, etc.
Think about all the transitions of "stuff" that an average family with 2 kids will need. Maybe one of those kids is a toddler, maybe another one is a little older and plays baseball. Somehow you gotta pick up the toddler from day care after work (diaper bag, maybe a stroller, car seat), and the older kid from school (books, projects, instruments) and get the older kid to baseball practice (bat, glove, maybe a couple balls). Plus you have your own stuff, maybe a laptop bag. You've gotta transition all this stuff all over the place without ever leaving anything in a car? You're gonna carry your laptop bag, your kid's school stuff, and all the toddler equipment to baseball practice? God forbid you have to do some grocery shopping on the way home after baseball practice. That sounds like a nightmare.
I agree that families with small children have a need for car-as-storage, but that passes after a couple years (per child). I'm not so sure about sports. For hardcore athletes, then yeah. But for your weekly biking or skiing or surfing trip, the equipment can be hauled on and off larger car-as-service's hired for the purpose. The rest of the time, store the equipment in a fraction of the space you would use to store a car with the equipment in.
Disclaimer: I was never a regular in any big-equipment sports.
If I'm wrong, well, like I said owning a car might still be fairly popular when they self-drive.
Any sport that requires an external rack for equipment like bikes, kayaks, or skis is a major hassle with rental vehicles. Sure some rental agencies already offer vehicles with racks but dealing with all the various options and configurations becomes a huge problem for logistics and inventory management. So they often don't have what you want when you actually need it. I'll keep my personally owned vehicles regardless of cost.
