Ask any individual who his or her favorite character from a given book, movie, or TV show is, and chances are that it will be either a supporting role or a minor character. In few cases will a person admit to favoring the main character, no matter how interesting or easy to identify with he or she may be. There are two reasons for this: protagonists are unlikely targets for pity, and tend to bore the readers/viewers.

No matter how complex a persona the main character may have or how developed he/she is, that fictional entity is likely to bore people. Not only is it less than unusual for one to immediately dismiss his or her neighbor's preference for a leading role as "boring," or even indicative of a lack of creativity or willingness to give a second thought to the other characters, but the very level of complexity so characteristic of protagonists is the primary cause of their tendency to arouse boredom in the readers/viewers. Since his or her persona was so thoroughly explored in fiction, very little is left to the imagination of the reader/viewer. Practically everything there is to know about him/her has already been established as fact in his/her respective fictional universe, and hence little to no room is left to speculation. No matter how fascinating a person the protagonist may be, it's simply more interesting for the reader/viewer to ponder the background and character of the more minor roles. Due to their status as minor roles, the lesser characters are generally underdeveloped, and for one to create their own backgrounds for. There's a far greater range of possibilities for the backgrounds of roles who haven't been fully fleshed out, as proof to the contrary of whatever the readers/viewers have imagined is scant to nonexistent.

People may also pity the lesser characters, despite their status as fictional entities, for being cast into such minor roles. This explains, for instance, why Blaise Zabini is so absurdly popular in fanfiction. Until HBP, the only thing the readers knew about him was his age, sex, and house--and even today, some people are still blatantly ignoring the second one--not only is there more room to work with, but to some degree the fans feel bad about how Blaise gets hardly any attention at all (even after HBP), while other students in his house and year *cough* Draco *cough* have whole chapters written about them and are given more significant roles as short-term antagonists. Speaking of which, some readers and viewers may also feel sympathy for the villains, and view them as simply misunderstood. After all, it's not pure coincidence that there are so many Snape and/or Draco sympathizers. The protagonists have already been showered with attention; after all, the story is focused around them. Surely the poor, underdeveloped minor characters deserve some attention, too. It's not their fault the author/creator made them such flat characters. Of course, the vast majority of readers/viewers are fully aware that the "pity characters" they're devoting so much attention to are not real, and are thus unable to care one way or the other about the roles the author/creator cast them into. Most people on the planet know the difference between fantasy and reality. Generally speaking, people develop emotional attachments to fictional entities not because they actually believe that the characters are real, but because they enjoy imagining how they would feel about their role in the story, or how much they would appreciate all the attention from their fans if they were real.

The readers/viewers may pity them for being cast into such insignificant roles. They may enjoy mulling over the possible backgrounds for the less-than-fully-developed characters. Some may even do both. Either way, lesser characters in fiction have a greater ability to capture the imagination of their viewers and readers than the protagonists the authors/creators devote so much attention to. It's this lack of attention that the authors/creators devote to them that captures the readers'/viewers' interest. Without the room for speculation on the minor characters' lives outside of what the author/creator has established as fact within their respective fictional universes, or how they would react to the attention from fans, people would barely give them a second thought. They would be deemed boring, and rendered unlikely candidates for a person's favorite character.