One of the boards they closed was tied to Woman's Hour, and was mothballed because it was too popular - the BBC argument was that because they employ staff to moderate the boards (*) and were overloaded by the numbers of posters concerned with topics on WH.
While I can understand (with trolls etc) there is a need for moderation (and perhaps some hours when threads cannot be allowed to get out of control given the global reach of the BBC and thus more likelihood of offence that might even cause a diplomatic incident, given the BBC is the "state broadcaster" in many eyes, however independent the UK service is, World Service is after all, funded by the Foreign Office), I do feel they could do it without reading every post but just looking into complaints.
The Archers boards may have more posts (I don't know, not a regular on any of them in the last 5 years) but what was really unfair was that 'The Choice is Yours' board moderator banned topics which had come from the WH radio show.
I had never looked at the WH board, but clearly when it was closed it left nowhere apart from Choice is Yours as a place to post about the day's broadcast...
I suppose it might have led to benefits for some other places (such as MN) when topics could not be discussed on the BBC's own message boards as the moderator would just delete the threads... and stifle complaints about having done so.
(*) 'opening hours' are a reason why most have only been usable during office hours, so one cannot, for example, criticise Today while it is on air!