Niia is right, Blizzard has confirmed they lowered loot drops, what was once approx 5 drops for a raid of 25 people per boss is now approx 3 per 25. Also in M+ if you miss the time on the key only 1 piece drops compared to 2 in BfA and if you time the key 2 pieces drop compared to 3. (You do still get more loot however when you time 16+ keys or higher).
EDIT: its per 20 player raid group not 25, here is the blue post regarding raid: