You don't need just the switch. It needs a housing, a cap, lighting, wiring, and connectors at the other end of the wire too. And all this needs to be designed

You don't need just the switch. It needs a housing, a cap, lighting, wiring, and connectors at the other end of the wire too. And all this needs to be designed in a "waterfall" style, with long lead times. Overall, a virtual button is going to be cheaper to engineer and manufacture than a hardware button. It's not big, overall, but these small savings accumulate over the whole vehicle.