They don’t tend to do a lot of expansions for games that aren’t selling well (because expansions sell worse than base games). I’ve never heard anyone recommend Fallout as a multiplayer boardgame, and I suspect most people don’t buy them to play solo. So I would guess that in this case, the base game probably sold well for a little while due to the license, people realized it had issues, and interest died down. My understanding is that Atomic Bonds also bolts on coop play, which might revive some interest. Maybe it’ll get more content then.