If a hostile mob is spawned or summoned and falls to its death or is killed. It will not drop loot. But a peaceful mob will drop loot.
Reason:
Has something to do with the entity view distance it seems.
Reproduce:
MC-137084
Hostile mobs not dropping loot when in view distance.
Resolved
Invalid
0
These mobs are despawning before they hit the ground, because you are further than 128 blocks away.