I don't think DF-9 was ever "not fun", but, for me at least, the issue has always been game-breaking bugs that forced me to start my game over. I think the difficult thing about a game like this in Early Access is that they need the game to succeed financially during stages of development where bug fixing needs to take a backseat to the development of game features. With such a small team, it almost seems now like Spacebase DF-9 was unfortunately doomed from the beginning. Most people are not going to buy into a game that they know is hardly playable, even if they think it looks promising.
I also think the surprisingly large number of "new things" and announcements that have come from Double Fine since DF-9 was put on Early Access have kind of buried it. Spacebase is a fairly niche title and I think it might have just gotten overlooked. Whatever the case, it's really sad to see the Double Fine game I was most excited about cease development. I hope the community hasn't lost all hope and some capable individuals expand on what Double Fine has put out. I think the game deserves more, for sure.