Why? We've been told for years that "people have changed their minds". All the evidence shows that people haven't, not by a large enough margin to justify holding a second referendum on membership, because if you did manage to get your way and overturn the first result with a slim margin, there is absolutely nothing to suggest the "losing" side would or should back down and be silent, demand another referendum, so the whole issue drags on and on with the UK still in this hokey-cokey limbo with the EU.
You want this finished and over? Back leaving with a deal and once we're out, begin a campaign for us to rejoin the EU.