The weeping and wailing began the night of the referendum. By the next morning we were confidently told by the press, Reddit, and Twitter that millions of Leave voters were already regretting their vote (and, as per TimPC's claim, were only now trying to find out what Brexit is), and that another referendum was thus the only fair/democratic/correct thing to do. (That even if such millions of Regretters actually existed that does not mean that a revote would occur is a minor technicality.) All part and parcel of the relentless effort since the referendum to invalidate its outcome by any means necessary.
It's pretty clear in retrospect that what drove the Labour collapse in 2019 (In some Red Wall seats—seats that Labour had held with massive majorities for 50-100 years—the Tories didn't have to gain a single vote to win) is both Labour Leavers unhappy about their party not continuing its 2017 acceptance of Brexit coming, and Remainers who disliked the idea (whether explicit among Lib Dems, or implicit among much of Labour) of ignoring a democratic vote in 2016. That's why another referendum was so unpopular, because no one believed that it would not be rigged against Leave.[1]
Those who in other circumstances might have supported a "People's Vote" didn't, because they saw it as yet another attempt to delay and prevent Brexit via Neverendums. I think Leave would have won another referendum conducted under the circumstances of the first one, but Leavers understandably didn't trust the People's Vote folks to implement another referendum in any way that Leave can again win. Not after 3.5 years and counting of shenanigans such as the Miller case.
[1] Even supporters of same, no matter what they said. That's why they were for it.
The idea that only ignorant people could vote against the EU is a popular meme amongst Remainers but actual polls have shown consistently there's little difference in EU knowledge between the two camps and to the extent one side has an advantage, it's those who wanted to leave who knew more.