Another reason some dealerships have closed or stopped selling the Triumph brand would be the reason one of the most successful Triumph dealerships in the country just a few years back and for a time a big supplier of big bore kits made for the air-cooled Bonneville line, South Bay Triumph in Lomita CA, would tell Triumph headquaters a couple of years ago to stick it up their, well, you know what.
Matt Capri, the owner of the shop and now just selling Nortons and Royal Infields and performing service on all brand of motorcycles, has told me that Triumph headquarters continued attempting to pressure him to take in many more units and much more spares inventory than what he knew would ultimately just sit for a very long time in his showroom and back in his parts and accessory department.
(...yep, seems the latest Triumph management is playing hardball with their dealerships, and this is spurring many of these closures)