Ukip in Britain, Front National in France, and a similar array of smiling europhobic racists and neo-fascists in Denmark, Austria and Hungary…
In most cases (except perhaps the UK, who really just doesn’t get that whole EU thing): because people just can’t be arsed enough to cast a serious vote, or cast a vote at all, at EU elections, and would rather “send a message” to their respective local governments by voting for the looniest candidate with a populist slant they like. Even if that means fucking up one of the only political entity that can truly make a positive mark on their lives in the coming decades.
Way to go, people.