Why Has the Role of the Sound Designer Become More

Why has the role of the sound designer become more prominent over the years?

A) Directors have learned how well they can cover up mistakes in shooting.
B) Sound design has simplified so people understand better how it functions.
C) Producers have realized that it is more economical to invest in a top sound designer than a cinematographer.
D) Motion picture sound has become more complex and increasingly innovative.
E) More men have entered the field, yielding higher salaries.