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.
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.
"Talent unions were highly suspicious of the threat to new work if programmes were repeated; indeed, before 1955 Equity insisted that any telerecording made (of a repeat performance) could only "be viewed privately" on BBC premises and not transmitted"
I'm trying to work out if there's a misunderstanding here, as this only applies to repeat performances, not presumably the original performance. So I wonder if recording at all at that time was not standard practise. I tried to work out in what circumstances telerecording was actually used for at that time, havent found much, but found this interesting white paper on recording the Queens coronation.
So telerecording was just a weird hack, and for a repeat performance you would expect to bring the actors into the studio again.