If Brexit is such a dreadful concept, why did Cameron give us a referendum,
From all indications, because he wanted to appease the hardline Brexiteers in his party and miscalculated the results of the referendum.
It was certainly a mistake, and a serious one, although it pales when compared to what came later.
why did both major parties state that they would honour it in the 2017 general election
Because they were major parties and probably wanted to remain being such?
You are here asking, in essence, how come a democratic system shows respect for the popular vote.
As things stand, you are calling people "undemocratic" for wanting a (quite necessary, mind you) People's Vote that may well reverse the result.
and why did 498 Mps vote for Article 50, which had no deal as the backstop?
You would have to ask them, I suppose. It stands to reason that many must have felt that showing reluctance would be denounced as attempts at sabotaging the result of the referendum and/or as failure to support their Party.
I have checked the list of votes. Here is the breakup, by my account. The totals are 498 for, 114 against. Make of them what you will, but I sure think that your question should be directed mainly towards the Conservative and Labour Parties.
Conservative - 319 for, 1 against.
Labour - 151 for, 40 against.
Labour Co-op - 16 for, 7 against.
DUP - 8 votes for.
UUP - 2 for.
UKIP - 1 for.
Independents - 1 for, 3 against.
Green - 1 against.
Plaid Cymru - 2 against.
SDL - 3 against.
Liberal Democrat - 7 against.
SNP - 49 against.
Source:
https://www.independent.co.uk/news/...s-labour-conservative-how-voted-a7558291.html
In retrospect, I must assume that many of them have since repented. We all ended up at least somewhat surprised by the way things turned out, did we not?
All the same, it seems to me that a more logical question would be "why did you elect so many MPs that supported Brexit so blindly" instead.
It is hardly unusual for major parties MPs to vote overwhelmingly in line with the avowed stance of the Prime Minister, their parties, or their own voter bases if they feel that it would be politically inconvenient for them to do otherwise, even if they believe or expect the proposal to be destructive.
Nor is it unusual for them to ignore qualified, informed opinions while at that.
They are, after all, ellected mouthpieces with no particular technical qualifications.