Surely the very reason we elect people to Government is so that they can ensure that the good of the country is paramount. If Brexit was, or is, not the best thing for the country why on earth did people campaign for it.
It is/was open to debate whether Brexit would be best for the country, which is why you had people (including politicians) prepared to campaign on both sides of the argument.

And now, having won the referendum how can those same people not tell us, the voters, the benefits of it.
While the referendum has been won, Brexit has not yet been achieved. You will have to wait to see the benefits, and some of them will be intangibles, such as control over our own laws and borders.