Same goes for the first Quatermass series - only fragments remain.
I worked at the BBC at a time that recordings were still wiped and the tape reused (I had to specify when drawing tape from stores for a recording whether it should be new or "serviced"). And tape is not easy or cheap to store, and at the time at issue it was expensive as well. Film was not much better.
The plain fact is that then, as now, huge amounts of material were being created, and there was no clear sense that everything equally deserved to be preserved for a grateful future - why would the future not prefer its own, better, stuff? We don't know that what we are doing is truly historical until long after the event.
Example 1: In 1970, the BBC broadcast a piece by Stockhausen, which was a directed improvisation by a full orchestra; it was only moderately successful, but I know that the final rehearsal for it was far better, stunning even, because I recorded it - but the tape is gone, as it was only recorded as an emergency backup in case something went wrong on the night of the live broadcast.
Example 2: I have just been asked permission, literally a few minutes ago, for the British Library to archive (as part of a website archive) two photos I took when fooling around as a student! How easy it would have been for me to lose them or throw them away at any time in the last forty years.
A last thought: Remember that until the late 1950s and into the 1960s, most programs were broadcast live, even multi-scene TV drama like Quatermass. The use of recording was not started to preserve programs, but as a means of time-slipping, on the one hand to enable programs to be edited and built up from separate scenes, and on the other to allow a repeat broadcast for convenience. Archival preservation was simply not part of the consideration, and this attitude only changed by degrees.
