Do you mean because they realized all of their options were shit, and so put off leaving the EU? That's the simplest explanation.
Leaving without a deal is a better option than the shitfest we're being served up.

Another not-so-subtle point is that public opinion has shifted towards Remain once people became educated on how bad economically leaving the EU would be.
I doubt it. Remember how the polls told everyone how Clinton would win and we'd vote to remain? Biased press. Leave will win another referendum, if it happens, which it shouldn't and won't.

"But, hurr durr we had a referendum 3 years ago that Leave barely won and nothing else matters." This refrain is really dumb. it's like saying we had an election a few years ago and so no-one can ever change their minds and vote for a different party now - the die is cast.
Referenda are expensive and divisive. You don't keep having them. Are you in favour of Scotland having another vote this year?How about in another three years? How about they keep voting until they vote "yes" and then stop voting? Is that your idea of democracy?

Brexit is not an inevitable outcome of a non-binding referendum.
Of course it's inevitable, and of course the referendum is binding, at least in the real sense if not legal. If we don't leave, the Tories will not win an election for a long time. That's surely scarier than leaving the EU, isn't it? I'm no fan of the Tories, but a decade or two of socialist Labour isn't particularly appealing.

Leaving without a deal is a great deal more likely than Brexit being cancelled.