It may be the most expensive 55mm, but Leica offers a 50mm that's $8K and another that's $11K.Honest question. I don't get why a well made lens with half dozen machine ground lenses of a particular shape and in one configuration can cost 10-20x what another well made lens with a half dozen machine ground lenses of a similar shape and configuration? How can the shape of a lens element or the coating cost so much more to produce? What is special about this lens that Canon, Nikon or Sigma could not reverse engineer (i.e. lens shape) and produce for $400?
Issue is not cost, but why would someone pay for it. What does it deliver that than "regular" lens does not - beside the ego boast of having the best and most expensive lens (based upon focal length)
What the Otus delivers is amazing performance at wide apertures. Forget the ego boost. It delivers something that a regular lens doesn't. The resolution numbers are even better than those of the Leica Summilux 50 (also $4K), which had previously surpassed all other fast 50's on Roger's tests (granted the Otus is a 55).
Of course resolution isn't everything, and for most of us isn't worth that much money. But this lens is without doubt very special. Why someone would pay for it: they want the photographs that can be made with it. Having special tools isn't just about having them, but about using them and making something special with them.