Why? Because in all the years I flew light VFR single pilot this only happened to me once, so it is bizarre to me. (insurance driven I was told) It also made the operation far harder, more stressful and less safe due to excess weight.
Why does a customer feel he knows better than the operator or regulator? That is bizarre.
But you seem to agree with my point that a clear distinction is made as to who does what which was my point. It matters not a jot whether the other is rated on type of course.