David
Mudcat covers whatever the people who contribute want it to cover. The current contributors have no control over who or what. There is no discrimination. Some of us are specialists in our particular field, and want to give out info and answer queries on what we know.
Those in the know rarely have time to spread into other fields. There is no deliberate exclusion. We do have plenty of experts in specific areas of world music but in the main they have solitary knowledge that no one else here has. Jack, Vic, Phil to name just a few. Their contributions are certainly valued but it doesn't always relate to what the rest of us are interested in.

UK, Ireland, US, Canada, Oz, NZ; that's one helluva big parish!