* monetary for the consumer (new features give manufactures an excuse to keep the price high) * environmental (because increased failure surface area causes consumers to need more repairs/upgrades) * safety (side airbags hurt visibility... Bigger cars are more dangerous ... generally safety features may make more people drive more dangerously [1]) * increased oligopoly (complex safety requirements stifle competition)
The problem isn't that there's no benefit, it's just that all of those "unintended" costs are actually boons to the manufacturers, so as long as they're calling the shots new features will just keep on rolling. Meanwhile, we just get more and more dependent on something that fewer and fewer really understand.