Most "audiophile" high end manufacturers, even the ones you read of all the time and might envision as being "really big", are relatively small companies that were started by guys with an intense interest and passion for 2 channel hifi. It has been my observation, as a member of that group, that most manuracturers, designers, reviewers, dealers, and importers never discuss headphone when they get together. Yet most of us are after the best sounding equipment with which to enjoy our products and test them with and we talk about speakers all the time, whether we are speaker manufacturers or not. Most industry guys love their great sounding, big, powerful, expensive, gorgeous speakes!
This would be the primary reason that most of these companies don't do headphone amps. Most have heard that headphones can be quite good but consider the main reason for folks using headphones to be that someone does not have a good listening environment, or cannot make noise in their environment. I only recently learned, after being in the industry for 30 years, that headphones can provide a great, emotional listening experience that in some ways exceeds that of speakers (for me).