What was your daily pax level? In my opinion, while you can start to feel the effects with just a few hundred thousand, you really need > 1m daily pax. Also only 4 hubs aint much. Try 40. Hub EVERY airport you fly to/from. I general only focus on green pax at standard capacities & prices till I get to this sort of level. Then I go nuts. It takes a lot of planes & a lot of time. Good luck.
The formula is simple:
Connecting pax per day between hubs = 0.002 * Total pax per day in+out of hubs
So if you have 50,000,000 passengers flying into an airport but it's not a hub, you get precisely 0 connecting passengers from that.
However, connecting passengers at one airport magically teleport to other airports. So 50,000,000 passengers per day out of a hub means you can get 100,000 connections out of ANY OTHER HUB, regardless of whether or not the two hubs are connected with a flight.
My daily passenger count is 370,000. I'm also operating the airline from Syria.. I cannot establish more hubs as you would in China or USA, I guess that's the problem then.
Thanks for your answers