It isn't clear how Tesla goes from "FSD" to "full automation". They are working on the "draw the rest of the owl" step.
Meanwhile, for Waymo to jump from level 4 to level 5 requires handling edge cases which it is actually not clear can be handled by the system Waymo has built. In huge swathes of the world, weather conditions are not conducive a system that relies heavily on LIDAR / roads change too much to be effectively mapped like they've done in very stable metropolitan areas like Phoenix and SF / etc.
Said another way: our existing roads are built for entirely visual agents (humans). Getting a system that heavily relies on non-visual sensing (e.g. LIDAR/Radar) to work well on a specific subset of those roads is clearly doable, but that doesn't mean it can be generalized to our entire automobile infrastructure.