Many, many northerners have "escaped" south as well actually, mainly with work as the main reason but there are lots down here nonetheless. And in terms of stuff most people like to do in their 20s - eating, drinking, generally getting entertained in one way or another - there is simply lots more to do down here and you therefore don't find yourself in the same old places. Not slagging off Newcastle because I love it and will go back when we're settling down but London gets a lot of stick simply because it's London IMO.
Capitol related anger tbh. It's prevalent in more countries. Norwegians not livining in Oslo hates Oslo, for no good reason really. Same goes with most Swedes I know regarding Stockholm as well. If you're not from there or have lived there you generelly grow up being told what a shit place it is filled with this and that and so on.
Then you also get the "natives" of capitols hating everyone not living there for no good reason. Basically people in the city rhinking everyone not there are backwards cunts and everyone not in the city thinking everyone there are cunts.