I can imagine the BBC bureaucrats making it difficult. I believe they pay an amount of needle time money for each recording played, and I'm sure they don't want to deal with piffling small amounts to tiny labels, or people with their own label. But is Pure Records (Kate Rusby) a major label? Or No Masters? I think not. It may be more to do with distributors.

Perhaps if 'minor' labels had an agreement with the BBC that they didn't want paying for needle time, being happy with the exposure they are getting, that might ease the situation. I hope that someone with actual knowledge might be able to pass on more information.