Your example is no different than demanding auto companies design every car to each individuals size, driving style, taste in body style, number of cylinders, HP,
A car is more complicated than a speaker. It has much more parts. With a speaker, the main area that needs to be tuned is the crossover. Customizing a speaker is much easier than customizing a car. A speaker is just a wooden box with drivers. A car has hundreds of parts.
Your argument is like saying we should just make eyeglass lenses in specific sizes because it would be cheaper that way. Unfortunately the world does not work like that. Eyeglass lenses are made to measure as you very well know. And the same goes for clothes. If you want a perfect fitting pair of trousers, you need them to be made to measure because none of the existing sizes fits you perfectly.
It doesn't matter if "High end [cars] can already cost tens if not hundreds of thousands of dollars. So there is plenty of money already going into the pockets of the companies." That money does not cover the cost of providing luxury cars to every car owner.
That is exactly the conspiracy which i am here to expose. If a speaker company can produce a speaker for $200, and it has no bracing and cheap parts, then it would only cost a few hundred dollars more to use ultra high quality parts. If you knew anything about the cost of drivers you would know that the difference between a cheap driver and a high end driver is often only about a couple of hundred bucks. Yet the price suddenly goes up by ten times. So dont give me this nonsense that there are costs to cover. You are speaking as though speaker companies make zero profit out of these high end speakers.