It comes in handy for organisms that happen to like feasting on decaying bodies through saprophytic nutrition. Paralysis enhances the chance of dying. Being a

It comes in handy for organisms that happen to like feasting on decaying bodies through saprophytic nutrition. Paralysis enhances the chance of dying. Being anaerobic limits their expansion. Thanks to the Great Oxidation Event, cyanobacteria caused. By the way, often humans and other multicellular Organisms are just battleground or collateral damage in billion year old wars between bacteria and/or viruses.