Taxis, available with e.g. a simple phone call, have existed since before telephones and cars really, and they still exist now even as ride-sharing has taken over. They will exist as Cruise rises.

They exist because they're a viable business because there is enough approximately consistent demand. That's not guaranteed to continue.

There might be taxis, but not enough for everyone who wants to catch one. It’s already difficult enough on rainy days.