I'm not including accents from places where you've lived, as obviously you will have had exposure to them that "teaches" them to you.
But for places you've never lived, why is it people can "do" some accents but not others? I can do a pretty good (IMO) Scottish, Irish, Yorkshire, Cockney, posh English, Texan and Californian accent. But i can't do a Northern Irish, Welsh, Geordie, Scouse or New York accent.