Well, a lot of it is because of the protection rackets that are ran to protect the Big Companies from having to deal with newer startups. We saw back in the '80s with the DeLorean Motor Company, and again with Musk's launch of Tesla Car Company. Some of these issues are primarily to do with the Big Businesses taking matters into their private hands, as happened with DeLorean, but most of it now has to do with regulations put into place by the Big Car Cos, with some input from what We, The People were actually asking for.
The Low Volume Motor Vehicle Manufacturer's Act in the Fixing America's Surface Transportation Act (
https://www.govinfo.gov/content/pkg/PLAW-114publ94/pdf/PLAW-114publ94.pdf), passed in 2015 allegedly allowed for companies to make up to 325 (replica) vehicles per year, but it wasn't until 2019 that the NHTSA finally got around to passing the regulations, after SEMA sued in 2018, and the government was supposed to do it's job in 2016. And it wasn't until 2021, six years after the law was passed, and five years after the job was supposed to have been finalized. That's just one law that I actually know about. There are many, many others that are all designed to either make it a serious problem for new automakers to start up, make it prohibitively expensive to do so, or to make other kinds of trouble for players who aren't already established.
The EPA is another agency that is making things a problem, which is actually why American vehicles keep getting larger and larger. During Obama, a law was passed mandating that the fuel-economy of vehicles keep going up incrementally, but the fuel economy is also related to size of the vehicle, so because we are currently up against a wall the economy based on the number of downstream-patches that are required, such as catalytic converters, DEF/DPF juice, EGR, and all the other stuff that is "required" but the fuel economy could be better and the engine could be cleaner if it were removed means that the auto makers can "cheat" the economy algorithm by simply making the cars larger. This also enhances their pocket-books, since larger cars can fit more "luxury" in it, and hey, since you're already going to be paying $50K for an "econo-" midsize, why not just add another $12K to it and get the super-premium LX package on top of that.
The regulations need to go away, and we need to get back to basics and be able to redesign something from the ground-up, and focus specifically on simply what is needed for the cleanest bang, and then balance the power to the weight.