The fact that your muscles can virtually ‘eat’ your fat is a fun fact of fitness training. Think of muscles as a machine and your fat as the fuel. This is pretty darn close to the perfect metaphor. If you have no or minimal ‘machinery’ in your body then you have no requirement for fuel, which means any fuel you have lying around (and most of us have plenty!) will simply stay there. Not cool!
Remember also that muscles are the reason you can move well. No muscles equals no movement which equals no life. This is why you must maintain muscle mass as you age because your quality of life is directly tied to it.