In many civilised countries they were enforced by law to publish their loot boxes odds.
Guess this is a “free” loot box, but as a nice policy they must publish the odds on every random item, or content generator so players can figure the real statistical value of a “high enough” number of items.
Maybe its not real random(), they may assign the loot based on a hidden ID tag=>list reference. Under this list, they may set a fixed amount of every item to be generated. We must know this anyway.