We figured out the first principles of fusion power in 1930s, but are still nowhere close to practical fusion power generation. The engineering difficulties are

We figured out the first principles of fusion power in 1930s, but are still nowhere close to practical fusion power generation. The engineering difficulties are just too great, and simpler alternatives exist which get much more attention, funding and optimisation. Similar might happen to vision-only self-driving. It might take a decade or two longer to develop compared to LIDAR-based approaches, and meanwhile LIDAR is only going to get cheaper.