Payne's characters are always (I can't think of an exception, but I haven't seen everything he’s written) fragile in a way that's very endearing. They don't even necessarily know they're vulnerable (like the Margot Martindale character in Paris Je T'aime, with her bad French accent and idiom, struggling to express a very heartfelt, deep love for the city). Even when they're brash (like Tracy Flick in Election or Jack in Sideways or the Kathy Bates character in About Schmidt), their brashness is (they think) their best defense against accepting or showing their fragility.

Imo, likability is more of a crutch for weak writers to distract from a flat storyline than a requirement for engaging the audience.

In Payne’s stories, you relate to everyone in the movie, not just the protagonist. He has a true love for humanity, coupled with a profound sense of its flaws.