I saw a video that was posted when 1.4 was first released that showed the graveyard biome doesn't work (background doesn't change/mist doesn't appear) when too close to exact world center. If your tombstones are near world center (and no sunflowers are nearby/on screen), then I assume this is the reason. I also think that it was/is intended.
Possibly the center of world being immune to graveyard change only applies to the Forest, not sure. But also, it is only the exact world center that has the "immunity", like when within the 60-ish tiles centered on the original spawn point (so when 30-ish tiles away from center). Just pointing out that you can still be near the center for the graveyard biome to form, just not right at, otherwise it will fade out the closer you get to center; at least if it still works like how it did at 1.4 launch. But ofc, yeah, very well may just be sunflowers.It must have been because Sunflowers. Me and my friend had a world in 1.4 that generated Jungle near center of world. Since it was MM we died few times fighting off jungle enemies with copper swords. Graveyard biome formed despite it being center of the world.
Oh thanks I didn’t think about that"This video is private"
Also do you have Sunflowers in your town or near the Graveyard?
If so remove them.
They cancel out the Graveyard biome.