a) because they have fear to compete or fight with materialist in material world.
b) because they are lazy & no strength to compete with materialist in material world.
c) because they are on the path back to Godhead, back home where everything is eternal, full and blissful.
d) None of them.

The correct answer is
c) because they are on the path back to Godhead, back home where everything is eternal, full and blissful.