because people dont generally see expensive gas as the norm, just an exception. Gas also skyrocketed in the 70's, leading to all that environmental shit and generally shitty cars. But it became cheap again for the next 2 and a half decades.
Also there's the fact that environmentalists and shit have been predicting "running out of oil" for decades, and then we just find more, and increasingly, there seems to be a theory that the Earth just generates oil, and there isnt only a limited supply created by ancient plants and dinosaurs, or we definitely would have run out already.
Also it's a cultural thing. Europeans always gravitated towards smaller, fuel efficient cars because they live in big cramped ancient cities that were never meant for cars to begin with.
in the US, there has always been the mentality of "bigger is better", especially in postwar America, where the country was rich and prosperous. And so car culture followed suit. big cars, with big engines. Handling? Turning? who cares, most American roads are straight lines anyway, and there's tons of long stretches of highway, where a large car with a large engine can be right at home. And while in Europe, big cars with big engines were usually the exclusive domain of the wealthy who wanted a toy, in prosperous big-road America, Automakers decided to bring that to the masses, creating the Muscle car. A sporty performance car for the working man to have some fun.
that sort of car romanticism has become ingrained into the American culture, that when there's a spike in oil prices, smaller, fuel efficient cars with small engines become popular for economic reasons, but people still really want a bigger car. So when gas drops down, until the industry catches on and up to that desire, people start snapping up older big cars, which is why when gas collapsed, you now see Hummers and Panthers everywhere again, as people are starting to sort of revert to "normal".
TL;DR it's an American culture thing.