I am taking a guess here but I think it makes it easier for them to do their lines as opposed to say being in the grass where they have to be more scattered due to the blades of grass.
Ants are cold blooded creatures. Concrete heats up faster and holds heat longer than other ground cover, making it a more productive environment for the ants. Plus they can burrow under it to build their nests and be very protected.
I worked at a bank that had an ant problem. After year of trying to find the nest they finally took up the concrete at the entrance to eliminate the nest and then repoured the concrete. Thankfully there were two entrances so they didn't have to shut down.
Surprise Ants have an attraction to life.