Earlier quoted context omitted.
The BBC used to have a policy of wiping tapes for reuse, seems crazy in retrospect but there you go. Sometimes people just don't realise what they've got.
The BBC did that to save money for new magnetic tape used for archiving. They thought that parts of their archives were just not valuable enough to preserve and chise to overwrite them instead. Unfortunately, some of the overwritten material turned out to be much more interesting and valuable in retrospect, for example a host of Doctor Who episodes which are now lost completely.
And video releases weren't yet a thing even if the rights could have been secured, so the apparent value of these archives was minimal.