Coating or parkerizing a blade is less expensive than putting a satin finish or mirror polish on one. Unlike bead blasting which makes the blade rust easily, parkerizing and coating also help prevent rust. I prefer a satin finish or mirror polish on knives I buy to look at but if I buy a knife to use the looks don't matter much. Actually if I could choose between a satin and black blade on the same knife at the same price I'd choose the satin, but that would still be based on looks and I wouldn't mind getting the black one. I don't see the point in spending extra money on cosmetic variations on a knife I buy to use.
If you look at the Busse site, for example, you'll see that you can choose the finish on the knives you want and a satin finish costs more. If the idea behind coatings were to make knives look "tactical" and sell more, wouldn't they charge more for the black coated ones?