Since you asked the question here is what I think drives them out the door.
Latest must have trend, expense is often mistaken for quality or even necessity, 'my mate has one...', 'must be the best cos' it costs the most...' and lets not forget good old pose value!
Seriously, some of those higher end rifles are nice guns. They shoot well but are generally no more accurate than one costing hundreds or even thousands of pounds less. Having said all that its nice to own nice things.
Custom rifles range from a couple of grand up to 3 or 4 times that. They are not necessary either but again there is an advantage when you can chose the exact specification, dimensions weight and so on. You don't generally get that with an off the shelf rifle costing the same as a custom build on a Sako, Tikka or Remmy...
I am not against things like Sauer, Blaser or Merkel but there is a point with them that you are either paying for a name, over-engineering or cosmetics. None of which in themselves will make it more accurate. I suppose it comes down to what is more important to you???
So many of the custom actions built by engineers for accuracy are still based on a Remmy. Simplest of mechanisms. Two locking lugs! They work, are accurate and all the fancy wood or engraving won't improve that. So, why pay for it? Nice to own nice things or pose value I'm afraid. First reason I understand completely. Pose value I don't...