These vehicles were complex and expensive to build. As popularity grew more people wanted to enter races but couldn't due to the high cost of building a car. Open wheeled racing was seen as an aristocratic sport, one that the average man couldn't compete in. This didn't stop the people from racing though.
By the 1920s dirt tracks across the South East began hosting stock car racing events, often between Moonshiners who would race their souped up get away cars. Although modified, their cars were still based on production vehicles.
Similar to the development of technology induced by NASA in landing on the moon, NASCAR stimulated technological growth within the automobile industry.
Manufacturer's benefited from their participation not only by having a more refined product but by the marketing strength that came with winning races. Bob Tasca, a Rhode Island Ford dealer and racing team owner coined the phrase "Race on Sunday, sell on Monday".
Imagine if NASCAR didn't ban fuel injection and the industry adopted it way back in 1957 instead of the 1990s. What would an extra 40 years of fuel delivery technology do to cars today? The 1969 NASCAR season saw the rise of the iconic Plymouth Superbird, an aerocar designed with aerodynamics to give better traction and cut through the air better.
Aerocars were promptly limited to a 305 cubic inch engine which was small in comparison to engines of the time which were around 400 cubic inches. Imagine aerodynamic styled cars catching on sooner than the 1980s. Imagine how much fuel could have been saved had all this technology been developed sooner.
Regulation has gone as far that all cars, regardless of manufacturer has to have a 4 speed manual transmission, 5.8 liter naturally aspirated pushrod V8 engine and a solid rear axle.
This combination hasn't been sold in a production car since the late 1970s. NASCAR only began allowing the use of fuel injection starting in 2012. While NASCAR isn't the only franchise racing "stock cars" these days, it's one of the few who get steady manufacturer support.