Naturally, given a previous existence, my interest has always been the negotiation.
I think there was a general wish by May et al to technically comply with Brexit to satisfy the 52% but only just, to satisfy the 48%, compounded by a naivety that our previous "friends" in Europe would continue to treat us as friends in reaching a deal. So the mindset was not to walk away and pursue another model.
It then didn't help that eg Davis and Johnson are vacuous sound bites and bone idle.
If you want a good deal negotiation should never be done if you have a deadline. You need to believe that the other side will do you down if they can - they are not your friends. Etc etc.
When it became apparent that the French and Germans were determined to punish GB the clock had been ticking for a long time and it was then too difficult for the Govt. to admit they were on the wrong track, stop and rethink. A bit like fellrunners, "we are going in the wrong direction so let's run more quickly".
Way back on here I mused how Trump would have dealt with all this. Whatever you think of him as a human being (!) we certainly would not have ended up where we are now - but then not many people think Trump is a nice man to do business with.