Question

why we cannot hear each other on the the surface of moon

Answer 1

Because of there is vacuum in moon and sound needs a medium to travel which is either solid, liquid or gas.
And due to there is vacuum (no air or gas) sound cannot travel.
Hope it helps you ;)

Answer 2

There is no air on surface of moon.It is totally vacuum. Sound cannot travel through vacuum
So we cannot hear each others voice on surface of moon