Labour offered another referendum on membership, which none of other parties offered or were in a position to deliver, so the decision to leave could have been overturned if enough people wanted it to. A Labour victory would have given them the chance, regardless of Corbyn's stance.
The Liberal Democrats took an even stronger position, basically ignoring the referendum. But the LibDems are still out in the wilderness, and got very few votes. All they did was to highlight that Labour was not the anti-Brexit party.
The impression I get was that by 2019, Remainers were tired of fighting about it, weren't enamored of Corbyn's version of Labour (Brexit was only part of it), and weren't going to rush over the LibDems.
And that overall, Brexiteers were enthused. Probably for very bad reasons, but they genuinely believed them. As for the original question, they might have been nudged along by some foreign propaganda and targeting, but it wasn't anything that their own leadership wasn't encouraging them to believe.
