It isn't so much nepotism as it is inertia and support. For instance, Sterling have chosen to focus on brass banding in the UK and Northern Europe (Norway, Holland, Switzerland, Belgium). They are doing pretty well and you have someone like Glyn Williams playing Sterling and soloing even in a Besson sponsored Cory band. David Thornton has also done well as a Sterling artist. But Besson puts a LOT of marketing dollars into banding and artists on a worldwide basis that the smaller manufacturers cannot afford to do. It takes a lot of money and support to pull together organizations like NYBBGB, provide a set of instruments to a top level band, or sponsor the travels and performances of artists around the world. Besson have the wherewithal to do that, and overall, it is good for the industry. In Japan, Yamaha does so much more, having repair shops in many of the schools (at all levels) and supporting thousands of beginners, intermediates, and artists.
Given the backlogs at the custom manufacturers like Sterling and Adams, the current "system" doesn't seem to be overly broken.
Doug
Adams E3 0.60 Sterling bell - Prototype top sprung valves
Concord Band
Winchendon Winds
Townsend Military Band