Prejudice…and even outright HATRED toward original characters are not uncommon in the world of fanfic. Original characters are, often than not, frowned upon in fanfictions. Here are the reasons why:
1) For junior fanfic writers and noobs around the world alike, there is a tendency for original characters to explicit Mary-sue-ness and Gary-stu-ness. They are the ultimate saviours of the drama, and sometimes, even the biggest plot device to solve the supposedly unsolvable because he or she suddenly obtained or discovered a super duper power to conquer the world with his or her beauty.
2) For fans, especially hardcore fans, they might question why is there an original character (as a main character especially & usually) in the way of their oppas’ friendships. Questions such as these might pop up: “Who does she think she is to have our oppas’ attention?”; “Why is she so special?”; “Why is she the one who gets to change our oppa’s heart?”; and blah. I’m guilty of being that kind of fans sometimes, BUT it’s because the story and characterizations are not exactly rational.
3) It can irk some readers when the original character’s name is the same as an actual female idol, singer, or actress, especially if the writer uses the idol/singer/actress’s picture to represent the “original character” in the story poster. For example, I saw some names introduced in the foreword of some fanfics on AFF like this: Park Chanyeol, Bae Suzy (OC)…Seriously, Bae Suzy is Bae Suzy! She’s an actual person, not an original character from the writer’s head! Sure, the personality can be invented however the writer wants, but please don’t take away Bae Suzy’s name and face and call her an “original character”. Instead, maybe try to come up with an original character name for the original character. Furthermore, there is an unconscious level of sexism going on. I rarely see any original character that is male (it’s a totally female dominated business), let alone a original male character whose name is Park Chanyeol.
4) Even if the original character is well-written, there is always an initial assumption that she is a hateful Mary-Sue before readers even click on the story link because. In a way, I supposed it’s because it’s destroying the nature of writing a fanfic about people, story, or stuff that are already in existence, published, slave-contracted, or stamped. Therefore, actual publishing writers definitely have it good when compared to their fanfic writing peers in this aspect.