My guess is poor sales. They realized that the market for true adventure riders is very small. How many people take truly off-pavement tours where there is no resupply points for multiple days and so they have to carry 4-5 days or more of food and multiple days of water. Think people doing Round the World (RTW) tours. These bikes typically carry over 100# when fully loaded.
I have a true adventure bike, a Thorn MkII, that is a "go anywhere" bike in addition to way too many other bikes. The problem is while the Thorn can go anywhere, it is heavy enough that I only use it when I do tours like the above, which doesn't happen very much. Even then as I age (sucks), lugging very heavy bikes up a steep gravel hill causes me to quickly lose all desire to ride those types of roads since I am basically either coasting or walking. The bike is willing but in my case the engine is a bit under powered. Think of these type of bikes as a Ford F-350 Dually Crew Cab with an 8' bed. Great for when you are out in the countryside literally going overland while hauling stuff but not so good in city driving where most people live. Most people would rather drive a Camry or a F-150 with a short bed.
That said, if I were going to do a RTW or even an extended third world tour, I would use my Thorn. Other bikes to definitely consider are the Co-Motion Divide, Van Nichols Deveron (Pinon), or Surly has a few bike models that are used for RTW tours.
Gravel bikes are somewhat similar and are very popular with new riders right now.
As far as finding your dream bike that is no longer made, there is eBay. Just do a saved search and it will automatically notify you when someone is selling one. For instance, there have been 4 Trek 920s sold on eBay in the last few months. You just have to be patient.
Tailwinds, John
