These are usually full-custom boards, very low-volume, with many layers and fine pitch traces. The parts themselves may have thousands of pins, routed across a

These are usually full-custom boards, very low-volume, with many layers and fine pitch traces. The parts themselves may have thousands of pins, routed across a dozen layers or more. So the non-recurring engineering (NRE) costs are very high, and you don't get to recover them over much volume. Even at 10x the cost, the vendor is still losing money.