Gunna expand a bit on what Erode just said. The RP does not really need each faction to have player characters to work. It could work with a bunch of freelancers, or any faction really. I figured a lot of people would want to be freelancers because they get more freedom than any other faction. They can choose how to deal with any situation how they like with fewer repercussions. 

But the espers working for Gemini and Maverick Alternative get to enjoy making choices that shape those factions. As an example, you'll be able to help Veronica choose which monsters to hunt based on how threatening they are, while with Billy you'll get to pick the monsters that you feel need the most protection. Not right away, but as you earn your faction boss's respect, they will rely on your intuition more and more. The freelancers only get to pick from the operations these factions have already decided on, so while they do have more freedom, they have less influence on what these factions do. And that's where the appeal in picking one of the big factions comes in I feel. 

But every faction gets to beat up criminals and cultists, so you really can't lose.