Really high level nonsense, all modifiers are invoked any time any loot is dropped by anything.
The LootConditions result in most of those modifiers effects being skipped (because the conditions were false, and that includes things like "a zombie died? Well that wasn't iron ore..."), but they're still checked.
The point was to create a system that replaced HarvestDropsEvent in a way that was as data driven as possible and would layer properly so that multiple mods could modify the same loot table without conflict (eg. adding a new crop seed to tall grass).
As such its complicated to create, but it is more better than any other approach for all the reasons that those other approaches are broken.