They don't have to, but they want to. They could say they will not accept content that requires DRM, just like GOG does.
BBC is state funded so it should be easier for it (easier than for a for profit company like GOG) to not be evil.
BBC is state funded so it should be easier for it (easier than for a for profit company like GOG) to not be evil.
In fact, internal systems already exist for accessing any BBC programme from the last (n) years. There's also a system for schools and universities that gives you access to the last year or so of programming. It's pressures from external production companies that prevent these from being rolled out to the public.
However, there will always be rights issues until the state has complete ownership over all TV production - which is never going to happen.
(Also - what's 'evil' about content creators wanting to protect their intellectual property and income?)
What exactly is DRM protecting them against? It's not geo-blocking, that's done on the server. There's no "download button" that suddenly appears on iPlayer if the content isn't encrypted. So please remind me what protective benefits DRM brings the rights holders and content creators?
Keep in mind, it's trivial to screen capture video on any half-decent computer. Anyone "determined" enough simply needs screen capture software and then hit record.