Question

Why do the voices of men and women differ

Answer 1

The voices of men and women differ because these are the physical changes during adolescence.
Men have low pitch voice and women have high pitch voice.

Answer 2

There are additional categories for operatic voices, see voice type. This is not the only source of difference between male and female voice. Men, generally speaking, have a larger vocal tract, which essentially gives the resultant voice a lower-sounding timbre. This is mostly independent of the vocal folds themselves.