Comment It's all about the costs (Score 1) 120
Automobile companies make a large number of vehicles - both GM and Toyota make around 10 million per year. Saving just one dollar on each vehicle adds millions to the company profits.
Something as simple as the extra wiring to create multiple data busses in the vehicle could add a couple of dollars to the vehicle cost. The auto makers will not do it unless it is mandated (either by law or their legal department fearing lawsuits) or they see some sort of a competitive advantage (somewhat unlikely) or there's a PR disaster.