How come a lot of Northerners have the assumption that Southerners are rich/posh/stuck up when there’s so many just as deprived areas down South?

I mean I’m as Southern as it gets (Portsmouth) and literally live on a council estate haha, I can’t imagine ever considering myself as rich or posh, and when I think of areas like Southampton and Essex and so much of London, I don’t exactly think wealthy and prosperous, to say the least….