It has more to do with the American war strategy in general: air supremacy is just the plan, and America has a lot of tools to root out AA and destroy enemy air forces. Compare to someone like Russia who is explicitly choosing not to dominate the airspace and relying on artillery for its fire support, and as a result has different focuses.

It doesn't have zero defense against AA- as a commenter upthread pointed out, this picture is literally showing it launching flares against heat-seeking missiles- but it's not something that's designed to work only when fighting non-peer forces, it's essentially capitalizing on the air supremacy that other components of American forces will be creating.