As it is a licence and a bloody expensive one atm. The % of UK citizens joining are reducing rapidly.
More importantly for a government system. You can see the BBC requiring a licence to set up an account. This instantly makes it unappreate as a giverment distribution and communications system. As wealth has a huge input on access.
Honestly the BBC seems to be hanging on by a thread atm. It has lost a huge amount of trust. And many brits just find the cost vs service much more questionable then in the past.
PS this was the tories intent. But hard to see labour current doing anything to fox it.