Sometimes a chunk of metal is easier to get than a how many barrels of such a fine powder, too. Powdered metal isn't exactly straightforward. There's a lot of ways that the process can go wrong, and leave contamination in the powder from tooling and transportation. On the other hand, a billet of most alloys is easy to make any size, and a lot cheaper in most cases, and can give much more repeatable crystal structure.

Kinda indistinguishable if it works all the same. Either way, nobody knows how the heck it works, but it works.