They built the most expensive solution (significant dependence on LIDAR) that scales the poorest (requires centimeter-precision 3D mapping of every street it drives on). Google Maps cars would need to do significantly more than they already do today on an even wider scale, and to be profitable it'd likely have to inundate you with ads on top of being the most expensive service.

...Meanwhile, the ADAS in many new consumer cars can pretty much drive itself already.

Waymo has to convince you their way is the "only" way to do self-driving cars, because nobody in their right mind would chose their solution otherwise.