You know, people like to repeat conventional wisdom even though they have no new evidence of information to share!
Why do we think hops only grow well up north? Not because of any controlled experiment, but because that's what farmers think.
Why do farmers think that? Probably because hops have always been grown at high latitudes.
Why have hops always been grown at high latitudes? Who can say for sure without doing an experiment? It may just be that beer was popular at high latitudes, and nobody ever really tried to grow them in Southern Europe.
Plant anyway, Southern Brewers!