This article titled The Cold Shoulder Given to Original Characters is geared toward Harry Potter fan fiction, but we think it pretty well answers your question. In it, HPFFHelp says:

Why don’t people trust original characters? Well, there’s an easy answer to that: they’re new, and people don’t like newness.

We read fanfiction to get more of the old, and even if people enjoy reading AU or Crossover fanfiction, there is a limit to their suspension of disbelief; there is an invisible line that authors dare not cross, lest they lose the reader entirely in their quest for uniqueness.

There’s a ton of good advice to writers of OCs in that article as well.

The same blog has another article called The Warm Embrace of Familiarity wherein they explain why they prefer Canon characters over OCs and describe some measures that can be taken by a fan fiction writer or RPer to believably incorporate Canon into their OCs, presumably to cushion the blow of “newness”.

Thank you for your question!

Do any of our followers have opinions on this subject that they’d be willing to share?