Why do in-state teams' fans hate each other?

Like the Jets and Giants, the Cowboys and Texans, The 49ers and Raiders? Why? especially since they are in different conferences and can only play each other once every 4 years, or in a super bowl. (wouldn't a 49ers Raiders super bowl be great for the Bay Area?) so why the hate? I don't hate the Texans, I know they are not a threat to my team anyway.