I think there are a few things to consider here.

First, when a human screws up, it's obvious who takes the blame for the mistake. If an autonomous vehicle does, who pays the fine/goes the prison? Putting the blame on the owner feels like it takes away a lot of the incentives to buy a autonomous vehicle, but I suspect the companies making these things don't want to be the ones paying out for their mistakes, and will probably lobby to prevent it if possible.

Secondly, this isn't just a vehicle thing, it's a technology thing in general. For better or worse, the expectations for safety and security are much higher for new devices than they are for existing ones, or for manual human driven solutions. Some of this is definitely driven or inspired by vested interests (like how pollution and safety regulations for renewable energy sources and nuclear plants are higher than for coal/gas power plants, despite the latter being worse in almost every way), but a lot of it is just humans being deeply skeptical of new tech and major social changes, even if the benefits of the new system clearly outweigh those of the existing one.