Probably due to the disparity in number of vehicles traveling over it. Consider:
Hartsfield-Jackson International (The world's busiest airport, according to KnowAtlanta.com) had almost 900,000 flights arriving and departing in 2016. By comparison (I tried looking for Georgia numbers for the Nearby I-85, but the closest I could find was numbers from South Carolina for that Interstate), the nearby I-85 has 47,600 vehicles a day going over it. That comes out to a grand total of 17,374,000 cars traveling over the asphalt a year!
In short, even if the weight is less, in the case of a car, the repetition of that much more instances of that weight applied, will put that much more stress on whatever surface you use. The problem you're trying to address isn't necessarily the lackluster stregth of asphalt...that compound is actually better for it to give some ways, so as to be flexible for the sheer amount of weight and number of instances of weight going over it. If it were hard and brittle, thermal expansion, along with freezing weather conditions and other factors, combined with all the weight of the cars going over it would grind it down into gravel much faster. No, the issue you most likely want addressed is the number of cars going over any one patch...which means either the road needs widening, or you need more roads, to reduce the amount of cars traveling over any given area of asphalt.
Asphalt prices ebb and flow.
Contractors are allowed to bid 'current market price' with a hedge on fluctuation.
Concrete prices are relatively stable. There is no provision for the contractor to hedge the price based on concrete cost.
Thereby: Asphalt wins the bid, despite little difference in cost after the fact, and often increased cost after the fact.
[–] 8424133? 0 points 2 points 2 points (+2|-0) ago
Runways are made of concrete as far as I can tell, and since there is an oligopoly on cement throughout most of the world I think you can guess why (expensive).