Because they are mechanically linked by the forks,how else are you going steer it if there is no connection.Now if the shake/ shiver is a unwanted one a steering damper is used to remove or control the feedback from the forks to the handlebars but still allowing movement for steering/counter steering.Incorrect tyre pressures,worn wheel bearings,fork seals(loss of oil / air pressure)head race bearings can all be a factor in excessive shaking but without seeing the bike in person a suggestion may be bad information,best get a mechanic to give it a check out..