FWIW, robotaxis are currently operating in about 20 cities worldwide; Waymo just received permission for robotaxi service in Los Angeles. It's a bit later than Musk predicted, but it turned out to be a lot more difficult than everyone originally thought.
And for the record, he wasn't the only one who thought they could have autonomous robotaxis running by 2020. GM, Ford, even Nissan said they would have them by 2020. So everyone was wrong, and they were all wrong because it turned out to be much more difficult to accomplish than anyone anticipated. But it is happening now.
Being 4 years late in bringing it to market, especially since COVID hit in 2020, isn't a big deal in the long run. Musk could have done what Waymo did and he would have had it 2-3 years ago, but it would have all the drawbacks of a system that only operates in precisely geomapped areas.