because it is two different end products.. one is worm castings.... they are used more like fertilizer not in as large amounts as you would use compost.
Two different kinds of worms also. I use red wigglers in my worm bin and in the compost pile earth worms live.
my bil used to bury the fish stuff all year from cleaning his fish about a ft deep in the garden area.. he would dig a trench and just fill with dirt as he went all winter...He could grow the best garden I ever saw.