Because we were pissed off being governed and told how to live our lives by a bunch of unelected, non-accountable, self-serving crooks intent only on lining their pockets at the tax payers expense. This is no exaggeration. The EU is elitist. You only have to look at who supports them: luvvies (actors), pop stars, politicians who aspire to positions on the gravy train, bankers and certain heads of big business conglomerates etc etc.
When we joined it was to be part of an ECONOMIC trading partnership (European Economic Community) but it has now morphed from an economic community to a POLITICAL entity, which aspires to become a European Superstate. I emphasise that the people at the top were NOT elected by the people, they are NOT answerable to the people and the people have no legal way of removing them no matter how corrupt, inefficient or incompetent they are. They live life on the hog with vast salaries, massive expenses packages, first class travel/hotels and countless perks, ALL OF WHICH ARE RIPPED FROM THE TAXPAYER'S POCKETS.
The UK has to abide by decisions and LAWS made in Brussels, which all too often are NOT in our own best interests. The EU is geared to benefit Germany and France with other countries including us, picking up the scraps. AND WE HAVE TO PAY THEM FOR THIS!!! In a democratic country, if you don't like the government or disagree with their policies, you can vote them out at elections, as we do. But the EU are above all this. They can do what they like, when they like and how they like with impunity because there is no mechanism in place which allows voters to get rid of them if need be. They are effectively UNTOUCHABLE.
If a proper Brexit deal is effected, it means that once more the UK can make its own laws, police its own borders and make its own decisions about immigration in terms of whom we are prepared to admit. People of value will be welcome. Freeloaders looking to live off benefits will not be. We will be free to trade with the rest of the world on terms beneficial to us and our trading partners without being hamstrung by EU rules and regulations designed to rein us in and benefit the 'big two', Germany and France.
I could write a book about this but I'll leave it there for now. I'll just say to the Remoaners that, if you think the EU is so great, why don't you just fuck off and live there and leave the rest of us to enjoy life in Britain the way it should be.