The answer is pretty simple, really - it is far too expensive. I could never justify even half what a 950 costs. In fact, I just bought a brand new Lumia 925, to replace my old 925, and I really couldn't be happier. I spent less than US$150 and got a phone that works brilliantly and now lasts three days on a charge again, where the old one was needing a top-up every day.
I can easily justify spending four grand on a laptop because I use it to earn part of my living but a phone is mostly just a toy with very limited utility beyond calls, SMS and a few handy things like comprehensive weather reports. It can't do a lot of even simple things, like replace my mp3 player, so I simply cannot justify spending more than about $300 on a phone.
I used to buy a new phone every year because they used to improve at a rapid rate but since I got my first 925 I haven't seen a newer handset that offers anything worth paying for. The 925 takes stunning photos, apps start really quickly and navigating through the UI is buttery smooth. When someone makes a phone that can run After Effects and 3DS Max, I might be interested but until then it's just incremental improvements that I really don't need.