The BBC didn't sell it, the EFL have the rights for the Albion online and keep them for their Player product and licence the commentary from them. The BBC normally allow their radio stations to be streamed worldwide so don't routinely block their content for users.
But how the EFL then decide...
If the EFL wanted the BBC to stream live radio commentary via the local stations online then they would let them or charge them appropriately for the right to do so.
However they think, and have done for years now, that they can make more ££ licencing the rights as part of the various Player...