They used to have 2 chests and it would give 1 for each 4 players you have. But those chests didn't strictly contain 2 pieces of loot always.

So if you had 1 chest, sometimes you'd get unlucky and get just 1 piece and sometimes you'd get a bunch of things, because which chest you got was random.

Now it's the same system except the chests are combined. Which makes it harder to explain to people so the easiest way is with this history lesson.