That is each dealerships choice, looking at the few comments on this and similar posts suggests it’s an opportunity. I would point out I found 3 independent battery repairers in the same area.They might not have the infrastructure available to become BCCs (battery care centres), they might not want to become BBCs or maybe they are but they only cater for their own brands, for instance, you won't get a VW only BCC repairing a Seat, Skoda Audi etc.
Part of the issue is oems haven’t pushed for joint repair centres, there is no reason why there can’t be a vag repair centre, the powertrain is pretty much the same. The workshop mine is at has 2 big vag dealerships where the seat dealership is that couldn’t fix mine.