Did you explain that much of the high-end mtb cost is in engineering it to be as light and efficient as possible using some fairly exotic materials?
Most of the moto cost is in the engine. The rest is pretty agricultural compared to the Yeti.
There may be economies of scale in favour of the moto too, but I have no idea how many of these they produce compared to ultra high-end MTBs.
Ultimately, there are enough competing manufacturers to ensure that pricing is reasonably competitive. There is no monopoly going on with MTBs. But the diminishing returns on top tier builds like this Yeti are very high.