Why do designers/manufacturers...?

IMO they try to sell their product for the least dollar amount vs their compitition.
Regardless what they supply with their products the buyer will still personalize it.

I think a few things come into play here. One, they want to assure the buyer that they design is optimized within the component itself. By admitting a power cord or feet make the difference, would admit a shortcoming within. Although some have added upgraded feet and called it out in the sales information. Two, I think they realize that a system synergy and environmental influences can alter the designed sound goal. Three, maybe they feel that their design can't be improved upon with PC's, fuses, feet, etc. But I really think that they focus on what is in the box and leave the rest to the consumer to experiment. And the benefits are realized by the cable, shelving, fuse, and other aftermarket manufacturers to exist. Or at least in my opinion.

I'm thinking that most mfgrs. see very little value in the tweaks that are heralded by many audiophiles. If the stuff really worked, especially the cheaper tweaks, you can bet they'd be incorporated into the design....

-RW-

I think it's because most manufacturers realize that accessories like cords, fuses, and isolation components are personal tastes and synergy related items.

Many manufacturers use these devices when displaying their wares at shows, they have their own personal favorites. However, they are smart enough not to force their tastes on aftermarket gear that they do not manufacturer on to their customers. They allow their customers to choose these accessories to suit their own personal tastes, cutting manufacturing costs in the process.