It's because their play is noticeable in a way that angers most casual fans. They carry play, maintain good possession, and drive the other team nuts but rarely finish plays. They tend to do this while an ignorant coach absolutely buries them with a deployment that no other competent coach in the league would dare consider, against tough forward competition:
So when we lose a game by a goal, people remember the 4 chances that Larsson couldn't finish, not the fact that 2 of our other lines never even created a scoring chance despite getting handed heavy o-zone starts playing against the other team's bottom 6.