Why do radially symmetrical animals have no concentrated area of nervous tissues?

Jelly fish.

"Nerve Net"


They do (jellyfish) not have a brain, a heart, a central nervous system, a skeletal system and also no bones and no blood. Jellyfish move using a hydrostatic skeleton that controls the water pouch in their body to manipulate their movements.

As far as the why........That is how they are designed or if you like how they evolved. Enviornmental adaptivity would be the primary factor.

Phenomenal reading on the subject at this link:



https://www.cell.com/current-biology/fulltext/S0960-9822(13)00359-X


Members of infrakingdom coelenterata, such as jellyfish and hydra, have a simple nervous system called a nerve net. This is a set of neurons, connected by synapses or gap junctions, that communicate with one another. The nerve net is centered around the mouth, but there are no anatomical groupings of neurons. Some jellyfish have sensory neurons known as rhopalia which can perceive light or gravity.

https://en.wikipedia.org/wiki/Nervous_systems