The problem with the EU is that Europe is not a group of 28(27) equal nations. It's a group of 2 mega rich nations, 5 quite wealthy nations, and 21 poor nations.
Of course people benefit, but not the ones paying for it. I voted remain in Brexit as I travel and exchange funds, goods and services with the EU. I voted in my own interest. But many others don't have that interest. They feel they are paying for other, poorer countries to soak up money to help their own nations whilst sending their people over to ours for work.
If they're coming here, why are we sending money there? Why are we building a train line in Hungary when a vast chunk of working age Hungrians use the S-Bahn or The Underground or The Paris Metro?
Hungary has a train station, but no jobs for the trains to take them too.
Looking from my perspective, I see the EU creating frivolous, unnecessary crap and not creating jobs. You always see those ''funded by the EU'' signs on a train station or a roundabout or a viaduct or something. You never see them on a factory. A call centre. A shopping Mall. Somewhere that creates jobs.
That's the massive problem Brexiteers had. All the money went to the East, All the people came to the West and even after all these years that trend has never changed. So when will it? And if doesn't, how sustainable exactly do you think that is?