We don’t know how consciousness works enough to say they don’t. Having a brain and/or nervous system might not be necessary.

Hmm sorry but no, there are traits exhibited by conscious entities which we don’t observe in those which lack consciousness. This is a nice explainer on consciousness, note that it’s not saying anything about needing a brain to exhibit those traits

https://plato.stanford.edu/entries/consciousness/#DesQueWhaFeaCon

correct me if I am misremembering sth