Brexit is not intrinsically 'right wing', as Tony Benn would tell you if he was still alive. Corbyn was always anti-EU, as were most of his inner circle before the party made him compromise. Was Tony Benn right wing, is Corbyn? Why were they so suspicious of the EU if it is some grand left wing project? Is 'flag waving' Scottish nationalism right wing? It's been around for decades and hasn't been born because of Brexit. Are Catalans and Basque independence campaigns right wing? The desire to free yourself from a greater lump that you no longer think works for your benefit is as old as it gets. Why is it that when English people seek it it becomes right wing?
As for your question, it's being asked by alot of people on each side of the Atlantic. Could it be that working class people just don't think that Labour and the Democrats care about them anymore? They did a survey of Labour members back in Jan, and only 12% said that the party's main focus should be standing up for ordinary working class people and their values. The party now doesn't think working class people are a group that they should focus attention on, because they do not fit within the modern 'identity politics' ladder of oppression. If the people in the party don't think that representing and standing up for working class people and their values should be their main focus, what is the actual point of the Labour Party? The Tories and the Lib Dems very much prioritise the rights and aspirations of the middle and upper classes, so why does the Labour Party exist if not to better the chances of the people that need them the most?
This is why Corbynism took root in the party, because it now has a membership that is comfortably middle class (around 75% in the ABC1 demographic) and doesn't actually need a Labour government to make their lives better, so they persisted with playing purity power politics with internal enemies whilst the working classes looked away. This has been happening for 25 years, read Paul Embery's stuff on this. He's a firefighter, union activist, Labour member and he barely recognises Labour as a party of the working classes anymore. I attended many meetings and put my heart and soul into the party and realised people were more interested in which wing of the party won a seat on the NEC than they ever were about working class issues. Who are the people who deride Brexit voters the most? The great and good of the Labour liberal establishment. The people it should be fighting for, or at least trying to win back, derided as racists, bigots, etc. That probably shows you why alot just turned their backs and went the other way.
Am I happy about that? No, I'm actually heartbroken that the party lost touch with people so much that they opted to vote Tory just to keep Labour out. But it happened, and Labour and its members and supporters deserved it.
PS - I'd be keen on keeping this open as an off-topic politics thread post Covid, it's fun even if we do all end up squabbling!