Because that’s not really what’s happening? A portion (roughly 50% of the electorate) votes to leave on June 23rd 2016. Since then several polls have shown that the electorate would vote remain on a revote (and some have shown they’d vote leave again, source:
https://whatukthinks.org/eu/questions/if-a-second-eu-referendum-were-held-today-how-would-you-vote/ ). So the question can reasonably be asked does the electorate still want to leave? The other half of your framing, “the elites” are preventing it from happening, is also problematic. One, because “elite” is a pretty nebulous word that implies that politicians (and possibly others? again, nebulous) are part of grand scheme against the electorate. Boris Johnson, the prime minister of the U.K., is apparently not an elite though? This seems like the line of thinking people who bought into “drain the swamp” had when voting for an amoral conman with a long history of corruption. Two, these politicians are elected by constituents to represent them. In the 2017 election parties that opposed brexit or think a revote should be held on the net gained seats. Which implies the electorate wanted more representation from those who opposed brexit. If the electorate overwhelmingly wants brexit, then why are they electing people who don’t?
The reality is the brexit question was posed in an objectively flawed manor. Do you want to leave the UK, yes or no? Doesn’t leave room for answers like, yes but only if we can maintain open borders with Ireland. Or yes, but only if we can maintain x economic deals with y countries.
The way democracy actually works is that decisions are made with an educated population making an informed decision. There is new information (the terms the EU is willing to give the U.K. for leave)so logically speaking it isn’t unreasonable to think a new vote should be held. But I’m not a part of the UK electorate so maybe I’m just an elite working to undermine them.