I'm not a synth designer or analog IC engineer, but from my limited knowledge:

Most polyphonic synths use individual chips for the main building blocks such as voltage-controlled oscillators, filters, and amplifiers, such as https://www.cabintechglobal.com/as3350-smt. Those are simple analog circuits, but the specific designs that work for synths are not really useful for anything else, so they are a boutique and expensive (relative to complexity) chip. Using those: N chips per voice x 49 keys x 3 voices per key = 147*N expensive chips.

There are also some "whole synth on a chip" available like https://www.cabintechglobal.com/as3394-smt at ~$10 each. So best case is ~$1.5k in chips alone for the core of this synth. Some other support circuits are still needed. Then $$$ for big PCBs and a big, noise-free linear power supply.

But even if we could drive the electronics costs down, that doesn't affect the per-unit cost of front panel controls, keybed, or the wood cabinet. Nor the per-unit cost of manufacturing labor, packaging, logistics. Nor the per-project cost of R&D and manufacturing tooling. All of these scale with size and complexity.

So it's no different from other specialized goods - the price gap relative to the "good enough" baseline will always be more than the performance gap suggests because the specialized version inherently sells fewer #units and cannot activate the same economies of scale.