my take is that they're seeing your offer as an invasion of privacy - they didn't ask to talk to you, would be happier without your interruption, you're invading their space, etc. these people probably have the same reaction to someone handing them a flyer - "f*ck off, i don't want one!!!".
maybe they've got some form of social dysfunction (mild Asperger's, for example) and just don't know how to deal with strangers?
i don't get it either, this is all that i can come up with. i don't understand what's so hard about saying "no thanks".