Apparently it's taking longer to shoehorn the new "Creations" paid mods shop into Fallout 4 because the Microsoft overlords are making them finish Starfield first. In all seriousness, the majority of BGS is working on the Starfield DLC because it will generate revenue. Patches for Starfield do not, and a next-gen update to Fallout 4, which has been marketed as initially being free to owners of the game, will only generate revenue from new console versions. The delay can therefore be attributed to the poor reception of Starfield (and the general state of the game at launch).