why does array modifier work with object offset?

Use CTRL+A > Apply All Transforms (on both meshes). If there still is some offset left when the 'other mesh' is not rotated, make sure that Object Offset is the only thing checked (so no Relative or Constant Offset!).

it doesn't work 

is there any other way?

Could you provide us with a screenshot?

Here's two a before and after

it hasn't changed at all

Uncheck the Relative Offset and put an object in the Object Offset field (it's still empty in the screenshots).

Then you should see only one of the arrayed objects, because all 14 of them are at the same place, but when you then rotate the 'Offset Object' the array should go round.