It could be that all the references say this nutrient is the quickest available to the plant out of all the Nitrogen sources.....perhaps you are confusing this quick nutrient
availability with water solubility
11. Blood and Bone meal - this classic combo can be found almost everywhere these days. However blood meal is very expensive. Bone meal can be even cheaper if purchased in 20 lb bags from feed stores. Since blood meal is totally soluble, it can be added to compost tea recipes.. With a NPK around 11-0-0, it has the highest total nitrogen ratio of all natural fertilizers, and may burn plants if used improperly. Steamed bone meal has a recorded NPK around 0-11-0. Usually steamed bone meal has a total N from 1-6%, 11% soluble P but 20% total P, and 24% calcium. Raw bone meal has more total N but none of the P is water soluble.
Have you ever smelled wet blood meal?