My two cents, I believe that it is a reflection of the market. It's what the market will bear, and we would appear to be in a booming headphone market.
The audio/video market has always been a place where purchasing above the mass market standard requires a fairly large premium for only an incremental improvement. If one wants a product that has low production numbers, one will pay a premium for that item. It's a luxury item, thereby produced on a smaller scale at a higher cost, and that fact has not changed.
I would postulate that the user market seems to have increased dramatically. Twenty years ago, one would buy a premium headphone for use at home, likely for kicking back on a recliner or sofa. Otherwise, one might own a second set of earbuds/portables for listening to a Walkman on-the-go. Now, smartphones are everywhere and fairly high-quality sound is inherent to that shift. Listening to music and answering calls becomes easy. For example, Beats takes off because people are actually willing to wear headphones while moving about in public! There are younger, wealthier clientele in front of computers for long hours with the opportunity and funds to plug in at work. As the market increases, there are new opportunities for expansion of product lines. The benefit is that if you can afford it, there are so many more options across the spectrum from a wider assortment of manufacturers, both large and small. The negative, of course, is that you will need to pay a hefty price if you want that top-of-the-line headphone, because the new flagship is now a step beyond yesterday's flagship in quality and price.