Quite a few people do fly outside FSO. For some, it's their only play session all week, or one of two or three sessions.
The reason it looks the way it does is because it's organized, they more or less know what they're going to be doing, and it's a scheduled thing. That's why you see many people there. The rest of the week, people log on and log off as they please so there aren't 130 of them in one spot at one time. 130 people logging on or off at their whim isn't going to massively affect arena numbers like it seems it would.
Wiley.