The Wellcome Collection's "Souzou: Outsider Art from Japan"

My friend and I would like to know: if the term "Outsider Art" just means what it says, why do exhibitions always make it mean something patronising? Something like, "Outside-Our-Culture-Oh-Wow-How-Quaint Art" or "Outside-Art-School-Wow-How-The-Hell-Did-They-Learn-To-Use-Paint Art" or "Hey-Let's-Give-A-Prisoner-A-Crayon Art."