Who’s job is it to turn their partner on sexually and why?

In the best love-making, each helps turn the other on.
But we are not mind readers.

We need to learn to read the other's body signals accurately - the deep stuff that happens at the unconscious or sympathetic-nervous-system level.

We are each also responsible for ourselves and our own pleasure:
what goes on in our heads,
how we shut down or open up to what is happening for us,
how we express it,
and how well we listen to and respond to the other.

Poor love-making is template sex, when a couple know each other too well and repeat the same formulas for years because they're the most efficient and take the least effort.

Both parties are responsible for that... what's the point in turning someone else on if you aren't into it yourself???

"Both" seems to be the obvious answer.