Minecraft 18w10a, Minecraft 1.13-pre1
The loot table function minecraft:exploration_map only works when used in the loot table of a container block, like a chest or dispenser. In all other circumstances, including
- Container entities, like chest minecarts
- Death loot tables
- Advancement rewards
the function has no effect, leaving a normal empty map.
Presumably, this is because the function is only able to get the current location when activated from a plain block.