Why did cars become boxy in the 1960s?

As far as really early cars were concerned, the boxy lines were mainly determined by the manufacturing technology of the day and the desire to minimise production costs. We take the complex, smoothly flowing geometry of the metal panels used to create car bodies these days for granted, but the technology behind producing the stamping dies is complex and largely the result of the demands of the car industry in the first half of the 20th century.

Streamlining was in vogue from the 1930s or so, largely in response to the public's fascination with aeroplanes and flight. Car manufacturers responded to that by producing cars that were streamlined (although the slow speed cars could travel at on the roads of the time and their hugely inefficient engines meant that reducing air resistance actually did little to improve performance or economy).

Things progressed in the usual way of manufactured products with things becoming more and more extreme as companies tried to differentiate their products from those of competitors and earlier models. But then the inevitable happened, and the fashion flipped to the opposite extreme.

These days, we're back to streamlining, and I imagine cars will continue to pretty much look as they do now for the foreseeable future. Because engines and drive trains are so efficient and because manufacturers are constantly trying to nudge up their fuel economy figures, reducing air resistance is important.

Something I find amusing is how car designers are now forced to fiddle around with little details to differentiate their products and sometimes the result of this is a circling back. When I was a kid in the sixties, there was a lot of chrome on cars. One of our cars is from 2002, and the only external chrome on it is the radiator grille and front and rear badges, while the only shiny metal inside is the door handles. We recently bought a 2019 car from the same manufacturer (Škoda) and there are chrome strips around the windows, a much larger chrome grill, shiny silver around the headlights, and bits of chrome in the interior.

Weren't a number of things boxy then? Like, even the architecture? 1950s brutalist buildings can be very 'boxy'.

I think it was mostly an appeal to nostalgia in the US but there were two major energy crises in the 70s that probably made it further evident that aerodynamics and fuel economy should come first moving forward, especially in case of history repeating itself.

I love old cars.

As you get older you grow more body hair

its easier & cheaper to design & stamp out a square piecea sheet metal than a curved one

computer aided design & microprocessor based manufacturing helped make it easier again