IL-2 content (ie campaigns) not available on steam?

Hi, I am confused why some IL-2 content on sale is not available on steam. For example, many campaigns do not show up there (Hell hawks over the bulge, Achtung spitfire, Havok over the Kuban, Ten Days of Autumn… maybe more?). I already own a bunch of IL-2 content on Steam.

Will these campaigns ever come to steam, why or why not? Can I purchase them from the website and still have them work with my Steam edition?