The gil farming is really only efficient for them because they're able to basically aggro the entire instance in a matter of seconds then AoE it down through the floor with no risk of death.
The gil drops are like a drop in the bucket for an average player compared to what you'd be getting from simply completing the MSQ or running roulettes due to them being split four ways (Which is not an issue for the bots since they're pooling their earnings together).