Loot Table Replacers

Issue

For whatever reason, I am unable to change currently existing Minecraft loot tables.
Yes I make sure to use the exact name of the loot table that vanilla used

I've attempted to use previous names of the same loot tables as well, which also wont work.

What I am trying to change

I am trying to set it so that grass and tall grass drop other items aside from just seeds using a loot table, however, the loot table doesn't seem to be applying

I have verified that I had it set up properly 

Registry Name: blocks/grass

Namespace: minecraft

Loot Table Type: blocks

For whatever reason, it just does not want to work the way it used to.

If anyone has any ideas as to why this may be happening, please do share.