Yeah, with the insane expectations that are piled on him, announcing it that early was a huge mistake I feel.
I suppose the problem was: first, OMIGOSHNOTCHMAKESASPESSGAME! reaction, which was timed terribly. If not for Minecraft, 0x10c could be moderately successful, with Notch being a no-name programmer and voxels not being a thing, but after Minecraft, indie developers just had a field day with 'lets take voxels and add a genre and a setting!' - cue voxel FPS games (Ace of Spades, for example), outright clones and yes, space games.
The announcement of 0x10c by the famous indie developer might have inspired some folks to make their own Voxel Space Games too, and they were coding faster than Notch's relaxed pace. Cue a number of games that did what 0x10c planned to be a pioneer in charging into the niche.
Second, a lack of any clear vision. Aside from the idea of 'let's make a cool space voxel game with massive multiplayer and spaceship building and nerdgasm to the nth power', the dev videos showed that at some point, it turned into 'AND LET'S MAKE COMBAT LIKE QUAKE, BECAUSE QUAAAAAAKE!'.
Granted, some things like that happened to Minecraft as well, but Minecraft was entirely unique in its style and a degree of freedom it gave to players. It anchored firmly in the richest bay (that being the twelfth bay, naturally) of the 'blue sea' - found a completely empty and rich niche, and that gave it a virtual immunity to developer's tendency to add features somewhat erratically - there was nothing else like that to choose from - until it became robust enough in features and popularity to become unchallenged, at least for a while.
0x10c had none of those, so it was much less shielded from competition from other games.