Their accident rate continues to decrease and things like quorum sensing and platooning are going to push them to be better than humans. You're never going to have a perfect system that never has accidents, but if you're substantially better than humans in accidents per mile driven and you're dramatically improving throughput and reducing traffic through V2X, it's going to make sense to fully transition.

I imagine some east Asian countries will be the first to transition and then the rest of the world will begrudgingly accept it once the advantages become clear and the traditional car driving zealots die off.