a.) Requires work. It means the artists have to move back to Grim Dawn to create item art, 3d models have to be made, if it involves new GFX then this also has to be made, then stats have to be come up for the item(s) in question and a place has to be found for it in game if throwing it into the already large, if not bulging number of random drop Legendaries isn’t preferred.
b.) Tangenting off the above, development for the game has slowed down. They’ve acknowledged this, while they are continuing to support it I imagine it is largely going to be in the form of balance patches and bug fixes, they don’t even know if more new content is going to come our way just yet:
At the most I would expect changes to what we already have rather than adding more on top by this point.
If someone does want to come up with new items, there is always the option of modding those in, e.g. Ceno has made some random item sets. Stupid_Dragon also experiments with modded items either for testing or exploring the different possibilities as well.