oh, if you play from the start (day 0) unlocking goblins is actually explained in the story now. As for the other hearts with no guests, chances are there were not for goblins, but for e.g. kobolds.
If you interact with a heart, you can check its requirements.
The way heart rooms work is not checking what you unlocked and spawning that, but spawning what was meant to spawn, and then showing players what they need to unlock.
If you play from the start day 0 is going to have no guests at all (reception not unlocked). After that, you are going to be able to unlock female goblins, and you are going to have guaranteed 3 days with goblins. From day 4 other guest types might be required to have any guests show up.