Well it's only my theory. But here it is. My theory.
At some point in the early 90s, every engineer at every car company figured out the huuuuuge advantage to be gained in cutting through the air easily. Put your car through wind tunnels, identify the perfect shape, and you gain huge MPG and huge acceleration.
At that point, the engineers explained to marketing ... And marketing understood that.
What engineering says and what marketing hears (after applying filters) is what happens. For example, 1930 cars all had blunt front ends. Theory: raindrop is an ideal aerodynamic shape. So 1930 cars were reshaped like raindrops. Because marketing wants to promote that (what we now know to be a) myth to hype sales.
Engineering and costs say the rechargeable has no advantages. But marketting is about hyping myths - ignore the engineers. Which is also why GM would not market their 1999 hybrid paid for entirely with government R&D money. Marketing will only market what people without driver's licenses can understand.
Every so often, engineering says something that marketing can convert into more sales. For example, in the 1970s, engineers said if we use low profile (square) headlights, then the hood could be lowered. Better MPG. So government regulators (who had created headlight standards when the automakers refused to) permitted square headlights that only GM cars had. Now Mr Jones was jealous of Mr Smith who clearly had a new car - because Mr Smith had square headlights.
Well GM then stacked the square headlights vertically on Buicks. GM engines had so low performance that the hood had to remain high. So square headlights did nothing areodynamic for Buicks - but increased sales.
That third brake light is another example. On all safer cars, the rear turn signal is orange. No confusion. Signals can be seen in all inclement weather. But then GM could not hype Mr Smith's new car to Mr Jones. All engineered cars already had the superior solution - orange rear turn signals. So GM got the government to install the third brake light so that drivers would not be confused by red rear lights doing too many functions. And so that GM need not run two more wires. Now Mr Jones had to buy a new car because Mr Smith's car had a third brake light. The crappier solution did not solve the problem. Promoted sales. And cost controllers did not have to run two more 'expensive' wires to the rear.
In every case, when the car is designed by bean counters, then marketing only hears engineers when it can hype the newest product as mythical innovations.
Name an innovation in a GM car in the past 30 years. None except innovations required by Federal regulations. If government did not require it, then engineers were not permitted to do it. This author even worked in GM factories. Engineers did not make decisions. Often, problems can only be solved by finding a union worker. He throws an arm salute at the corporate offices. Then as one said to me, "Let's go fix it right now." Engineer could not do anything until he had permission from bean counters.
Also why GM cars must have two extra pistons just to get the same horsepower. So GM cars cost more to build than comparatively equipped Mercedes Benz. GM cars even required wheel alignment that was long made unnecessary on partriotic American cars designed in Japan and Europe.
That is why NUMMI (that finally closed on 31 March 2010) could build cars for GM with only 1/4th the employees. And GM then refused to learn the lessons from NUMMI. Marketing only permits a new 'appearance' when it can be used to hype sales. GM cars obviously being some of the world's worst because engineers are not an asset - are only an expense - according to GM spread sheets.
Marketing only hears what it wants to hear - which is why GM still does not have a hybrid. Which is why the Volt must be hyped as rechargeable because it is nothing more than GM's first hybrid - while the competition is already making its third generation hybrids.
