What you're describing is a reliability nightmare. Human drivers 'depend' on road markings, but if some paint gets scuffed or a stop sign blows down in a storm

What you're describing is a reliability nightmare. Human drivers 'depend' on road markings, but if some paint gets scuffed or a stop sign blows down in a storm, things still work okay. For AI cars to be similarly fault-tolerant, they need to be generally capable drivers who don't absolutely need exacting external markers to get around.