First and foremost, I guarantee you if the ASOIAF didn't start out with the Starks, the average fan wouldn't loathe the Freys as much.   Freys started out from the bottom and become one of the top 10 richest houses. And Yet, no other 'historical' house have showed them any respect. They followed Aegon against the Hoares and then pledged to the Tullys as their liege lord. But yet, The Tullys always looked down upon them.  Regarding the rebellion, maybe half of the Riverlords sided with