Because things have significantly changed since June 2016, especially given the possibility of No Deal that was barely considered as a possibility then. If the government hadn't cocked up finding a post-withdrawal option so badly, I don't think respecting the result would even be as close to as big of a debate as it is.
Although given the claims that were made by the leave campaign at the time, the lack of clarity on what Brexit was ever supposed to mean, the vastly differing views on what the ideal deal was right from the beginning... You could have seen this coming from a mile away
