But so many of the little problems have been solved. Batteries are much better. Radio data links are totally solved. Cameras are small and cheap. 3-phase brushless motors are small and somewhat. Power electronics for 3-phase brushless motors is cheap. 3D printing for making parts is cheap.
I used to work on this stuff in the 1990s. All those things were problems back then. Way too much time spent on low-level mechanics.
You can now get a good legged dog-type robot for US$12K, and a good robot arm for US$4K. This is progress.