Trading factions are about camaraderie and organization. It's not how much you can make, but how well you get along with eachother and the tactics you can practice.
Roleplaying a trader or an escort is no different from roleplaying anyone else. It's not the trading faction that impairs your ability to roleplay, it's your undefined character.
I could be a Liberty escort that hates LSF and gives them a hard time, or an escort that always attacks slavers, etcetra. I can also be a trader that has the heart of steal and acts as a hero when pirates are around the corner, or someone who drinks too much gallic wine and loses cargo randomly or too much money in convoy gambling.
I could go on and on, but I honestly don't think the reason why people don't like trading factions is because of the RP or lack there of (allegedly).