Really? My adaptive cruise on my bog-standard GM Volt seems to have no problem seeing static obstacles with it's "primitive" radar.
My vehicle is doing adaptive cruise to the car in front of it--including on banked curves and in Los Angeles traffic--sometimes dense-sometimes empty. This means that it is working out which car is in my lane--probably via beam steering and corresponding to my steering wheel position.
This doesn't seem to be an impossible problem. This seems to be a Tesla problem.
This one discusses that the Volvo system has the same limitation, and implies that most others do too https://www.wired.com/story/tesla-autopilot-why-crash-radar/