[shaewest]

I would assume the issue there would be transport. It'd be cheaper to use "local cement maker X" than to ship from "remote cheap cement maker Y"

[narnarpapadaddy]

In the case of concrete there’s also a time component. Once you mix the cement and aggregate you have a few hours before it begins to set. The cement itself is already typically trucked in (a relatively small amount of dry, easily transportable powder).