mobRule Greifing true or false, mobs still cant pick up items

I'm trying to get zombies to pick up items, they wont, no matter if gamerule for mob griefing is true or false.

What I expected to happen was...:
that zombies would pick up items

What actually happened was...:
wont pick up items, no matter what game rules applied

Steps to Reproduce:
1. spawn a zombie or find a zombie on the map
2. drop items on it, maybe put it in a hole so it cant run from the items you want it to equip
3. proceed to not have zombies pick up items... ;-;