Well it takes assets from a product they're trying to sell, and gives it away for free to products that have already been sold. This takes potential money from them. It's not rocket science.
Instead of modding stuff into the earlier version, why don't you mod original stuff into the newer version (Rebellion)
You get the benefit of the new graphics, compatiability with the latest version of SOASE, and much more interest in your mod. Star/Clad get the benefit of more mods providing more interest in the game.
Taking stuff from the latest version and modding it into earlier versions, OR copying the design and modding it into earler versions is an asshole thing to do to a company that has been very supportive to the mod community in comparison to many other companies that prevent modding, or simply don't support it.
In addition, it's about as unimaginatave as can be to take assets from something you didn't make and mod them into something else. Stretch your capabilities and make something new, which is the true enjoyment and appeal of modding.