All wall types within the Basic Wall family have an instance property called Structural Usage, which specifies whether the wall is non-bearing or one of 3 kinds of structural wall (bearing, shear, or structural combined).
When you use the Wall tool, Revit LT assumes you are placing partition walls. Whichever wall type you select, the default Structural Usage value is non-bearing. To change the value, first select the Structural parameter. Then you can change the value of Structural Usage.
When you use the Structural Wall tool and select the same wall type, the default Structural Usage value is bearing.