I don't really know the state of the art in self-driving. But it might very well be that it wasn't the technology that changed in these past 5 years but the regulation around it as incremental changes were made to regular cars which have led to regulators consider that the technology was, after all, safe enough for these use cases.

Not that the technology hasn't improved, but with these things there might be many factors involved that might answer the question "why we have this today and not 5 years ago".