One is the reasons is the image, the other is the Adams mystique.
Adams, like other successful artists, marketers, hucksters; sold "us" on his process. (As evidence I offer his books.) Silver gelatin printing is only important in the market valuation of clearing winter storm because "that's how Ansel did it", its how the original was made. Anything else would be "a fake".
Elliot Erwitt and Steve McCurry don't need to worry as much about the exact how of processing as the Adams estate might.