why does being "materialistic" relate to being "superficial"? they go hand in hand these two adjectives? why?

When someone is materialistic, they focus on material items rather than relationships and caring for others. We see them as shallow because they want things for status.   When someone is superficial they are often considered shallow because they pay attention to material status—or a perceived image.  He wears a Rolex he is important.  

So these two words get used synonymously because they have a similar vibe. 

Superficial is face (Latin facies) value.  You can't always judge a book by its cover implies feelings, soul, are of additional or primary value. 

When bigotry moves beyond privileging either the material-object idolatry or the feeling-subject idolatry, its psychologism of idolatry is transformed into a Oneness of Source-realization, much as Plato, Plotinus, Husserl, and Whitehead realized and taught.

Related:  "Return to the One:  Plotinus's Guide to God-Realization;" "The Path of the Higher Self."

Because they don't have a language to talk about computer apps or smartphone apps, they talk about boxes.

Because the love and desire for material things is shallow and without any real meaning.