AS is hubcentric because the data that they use to drive everything is essentially mirrored off of real life data.
This means that because Delta runs hubs in Atlanta and SLC in real life, Atlanta and SLC in AS will have WAY more traffic than they should in any way, shape or form. What this means is that your job in this game is not actually to connect people, it's to emulate whatever real world routes exist as best you can (or at least better than everyone else). You don't have to operate a hub in Atlanta, but a LOT of people going through your hub will want to connect there for absolutely no reason, other than that real airlines use it as a hub.
This is sort of flawed, IMO, as we saw how Southwest completely ditched the hubcentric model in real life and nearly began to eat United's and Delta's lunches.
Understanding that this is how AS works is even more important for international routes. For instance, in real life there is not a single direct flight between LGA and LHR. They all connect through Boston, IAD and Atlanta. This means that there is NO demand for an LGA-LHR route in AS (essentially), even though any sane person would think there should be.
Don't think that "realistic economic model" means that it simulates an economy. It doesn't. AS emulates actual statistical data on behaviors of passengers in real life under the mistaken assumption that it is 100% reflective upon the passengers themselves, and 0% reflective upon the available choices in real life.
EDIT:
For reference, here are some real life hubs in the US:
United: ORD, SFO (asian international), DEN, IAH (for the old Continental traffic)
Alaskan: SEA, DEN, PDX
Delta: ATL, SLC, JFK (europe international)
Just off the top of my head. There are more, and IRL they have their own focuses, and that impacts what routes are actually reasonable in AS.