Reply received from the TARDIS:
For some reason, the BBC decided to destroy all the episodes of the first two Doctors
This comment is erroneous on two counts. First of all, not all the Hartnell and Troughton episodes were destroyed. Secondly, and perhaps more worryingly, some of Jon Pertwee's episodes WERE junked, though on nothing like the scale of his predecessors. According to the BBC, the reason for this was storage space. In the 1970s, when most of the deletions occurred, the BBC decided that it didn't have room to store copies of every programme it produced. Given the high cost of television production, old tapes were wiped and re-used and, amongst these, were episodes of 'Doctor Who'.
Now, insane though this may now sound, there was a certain logic to it all. Remember that in Britain in the 1970s, the domestic video player was pretty much unheard of, and the argument followed that, in the new era of colour television, no one would want to watch a load of old black and white shows from the 60s. Secondly, the 'Doctor Who' fan base was still in its infancy, and had nothing like the voice and influence it has today. Therefore, the deletions proceeded, and it was into the 1980s before anyone raised the alarm.
In terms of the first two Doctors, the greatest loss was from the Troughton era, with only six complete stories remaining. Hartnell is much better represented, though a complete version of the final episode of 'The Tenth Planet' is still a major omission. Meanwhile though it is hard to believe that some Jon Pertwee episodes were lost, all of them have fortunately been recovered in one form or another. However, I gather that Part One of 'Invasion of the Dinosaurs' is so damaged as to not be of broadcast quality.
Happily, lost episodes have reappeared from sources all over the world, including the almost-miraculous return of 'The Tomb of the Cyberman' from Hong Kong ten years ago. Added to this, the remarkable work of the unofficial 'Restoration Team' has done much to restore this old material to its former glory. As proof of the latter, I would recommend the recent DVD of 'The Aztecs' to those who don't already have it. However, I think that any realistic fan would admit that there are some episodes that we just won't see again. The BBC would seem to have tacitly admitted this fact by their release of the reconstructed finale of 'The Tenth Planet' a couple of years ago. I'd dearly like to be proven wrong, but I feel sure that if the hundred or so missing episodes were still out there, we'd know about it by now.
As a final point, we should keep in mind that not every episode of 'Doctor Who' was brilliant, and that there is, perhaps, a level of loss that we can tolerate. When I was a kid, I read Bill Strutton's novelization of 'The Web Planet' and was totally gripped. As for the video, I have only managed to endure it once...
"We are not of this race. We are not of this Earth. We are wanderers in the fourth dimension of space and time." Doctor Who-The Pilot episode