Why exclude unarmed builds from using heralds?

I first ran became frustrated by the martial weapon limitation while experimenting with concoction skills. There aren't very many tools in the game for unarmed bleed builds and to not be able to use the only bleed-related aura on a pure bleed build just made no sense to me. I had the same experience with herald of plague and poisonous concoction. I'm a poison attack build. Why can I not use a poison attack aura?

Any attack build should be able to use heralds.

With Much Copium,

Concoction user

Also, not having ANY form of proliferate on Acidic concoction is really awful.

Herald of Blood does work with unarmed if you have Hollow Palm Technique