Well the truth is, they have. It’s not night and day, as there are engineering and cost concerns that come with chasing improvements, and there IS a limit to how much power you can get from an ICE, but they are improved. But most of the improvements so far are weighed down, literally. Newer cars ar heavier, with more power output, and more features, and that all brings efficiency back down. All manufacturers could have 50mpg cars out ther tommmorow, but that’s not what the market wants.