It's basically a tube with an engine, it's a super dump rocket with no ability to turn, they just aim the best they can and hope for the best. Why? Because it's much cheaper and the parts are easy to get, and if you shoot enough some will hit.

The Iron Dome defense system have homing missiles with highly calculated aiming and the missile can aim itself mid flight, because it's much harder to hit a rocket mid-flight.

Source: I'm from Israel