There's a business argument to be made. (It's not a particularly compelling one, however.)
1) Considering all the segments Sennheiser plays in, I assume they spend a lot on R&D, and someone has to pay for it.
2) I'm sure the manufacturing cost of Gorilla Glass adds to the cost of materials.
3) The high-end market tolerates - and I use this word deliberately - products up to $6,000 (Audeze, Focal and Hifiman all sell headphones $4000 or more). So products "need" to cost more than $2,000 so they're considered truly hifi. At least that's my impression as someone who's never spent more than $700 on a headphone.
Now, personally, I think all three arguments are terrible. But it's the best I could come up with.
I'm just shooting from the hip based on what I'm seeing. But if anyone has any good explanation why that headphone is so darn expensive, I'd love to hear it.