As much as I'd love the advanced features of the Steam download system, I don't really think it makes sense for them to bother with it. I'd love to see the numbers, but I doubt the number of people accessing the game through Steam is a large percentage, and unlike the PS4 stuff (affects any and all PS4 users), utilizing Steam's download system doesn't allow them to scrap their own since so many other people don't use Steam at all for FFXIV.