That's honestly the key with a lot of A&R's.... To be honest, a lot of them don't have the ears to really hear an unmixed song and know the potential...
They also don't have the time, so when something is all muddy, they are just going to turn it off. It's shows lack of respect for your work and a lazy work ethic.
A half assed produced beat that's mastered, goes a lot further than a talented producers beat with a bad mix... People would be surprised how good some engineers can make the worst shyt sound.