I'm not offering a justification, here (I like value gear, DIY), but just for your consideration, here's how the industry might explain the strategy — and it's actually a stronger defense than it first appears.
The core move is to deny that very high-end audio is primarily a functional commodity. A Hermès Birkin bag is not priced according to the cost of leather and labor. A bottle of Petrus is not priced according to fermentation costs. What you are paying for is a constellation of things that resist cost-accounting: heritage, craftsmanship as performance, exclusivity, aesthetic identity, and membership in a community of connoisseurs. High-end audio manufacturers would argue they are selling something similar — not merely sound reproduction but a cultivated experience, an object of desire, a signal of refined taste.
They might also push back on the R&D comparison. Developing a novel transducer geometry, a proprietary cabinet solution, or a new output stage topology may involve fewer engineers than a Toyota program, but the intellectual labor is highly specialized and the market is vanishingly small. You cannot amortize development costs across hundreds of thousands of units, so the per-unit burden is genuinely and unavoidably higher.
The deeper defense might go like this: some goods are *constitutively* expensive, meaning the price is partly what they are. A $50 perfume and a $500 perfume are not the same experience even if the molecules are similar, because the ritual, the packaging, the story, and the social meaning are part of the product itself.
The vulnerability of this industry defense, of course, is that it partly concedes your point — at some level you are buying myth as much as engineering. Whether that's a scandal or simply how luxury markets work is a genuinely open question. I mean, are we going to start pretending that myth is not a huge part of a market? But it does explain the strategy, even if it doesn't fully justify it.