Probably because they would have to support tens of models and tens of millions of vehicles. Big car companies contract their head units out per body style, so

Probably because they would have to support tens of models and tens of millions of vehicles. Big car companies contract their head units out per body style, so one company may design the 2008-2012 head units and another 2013-2016. They likely have wildly different sensors, firmware update formats, etc. Bigger car companies prefer stability over features and don't design everything in-house like Tesla. Their shareholders also expect them to turn profits, which leads to risk adversion and slower product cycles.