You could think of it as being like Chemistry and Chemical Engineering. Chemistry worries about the properties of atoms, and how those atoms affect the properties of molecules. They worry about where the outer shell electrons go.
Chemical Engineering worries about "how do we make this stuff in multi-ton quantities without blowing up downtown". They worry about cost of raw materials, and disposal of waste products. They worry about pipe bursting strength.
In the same way, Software Engineering needs to worry about some things that Computer Science doesn't. (Maintainability is the big one that first comes to mind, though there are probably others.)
[1] Or "somewhat less inefficient" production, but the sentence was long enough already.
[2] And maintenance.
