Because Linear mode doesn't measure decibels, if I understand it correctly. Decibels are logarithmic (I.E. see the post above mine), where as linear is just that - linear whatever-the-unit-for-that-is. So 200 in linear does not equal 106 decibels. Simply put, 106 decibels (whatever you chose to number the linear scale at) is where the microphone stops distinguishing the volume.