Why not?

I have always wondered why if better cables produce better sound, as appears to be the consensus, I am not aware of any manufacturer that provides an aftermarket quality power cable with their product. If I am wrong please tell me. There may be instances I am not familiar with.

Wouldn't they be in the best position to test or design the optimum cable for their component? Wouldn't it be a great marketing angle to say to the customer does not need to worry or fret about selecting this expensive accessory.

"We know these cables show off our component to best effect and there is not question of listener bias or self interested market hype. We offer you the best cable to use with our components." 

They could make it optional if they wanted to remain price competitive. This same thinking applies to interconnects, especially with manufacturers who make multiple interconnected components. I pose these questions in all sincerity, not particularly wishing to stir the cable controversy pot. But because it is precisely the absence of this practice that most makes me doubt the objective superiority of the whole cable enterprise.

Mostly I would like to know if I am wrong and there are some examples of manufacturers who either include, offer or recommend specific power, interconnect and speaker cable for their products. Thanks community members for offering a place to ask this question that keeps gnawing at me.