Structure Generation 1.21.7

Heya, I am quite experienced with modding and all but getting into this worldgen and structure stuff.
I am trying to make a Nether Structure Generation pack.
I've attached my very basic outline but it doesn't seem to generate anything.
I know it says to "Instead of giving code, give an explanation". I am providing both for simplicity
Some things to note:

I have increased the nether depth to -128
I have a custom biome that spans the entire depth of y=0 to y=-128 called lnm:forgotten_depths
I have full custom generation there (in another pack, and yes I am loading this pack with that one)

It loads just fine but I cannot seem to get the structure to generate at all as when I run /locate structure lnm:blackstone_castle it finds nothing.