How to make creepers drop pigstep, etc. when killed by skeletons, but only at specific structures

I'm trying to make a skyblock map, and the pack I'm using as inspiration was built in 1.20 I believe, but when I try to update the loot table for creepers to 1.21 and modify it to use my specific structures, they don't drop anything. Here's the loot table I'm using so far: