Regeneration is not possible in all types of animals. Why?

(N/A) Regeneration is a process that relies on the presence of specialized cells known as stem cells or undifferentiated cells.
These cells have the potential to proliferate and differentiate into various cell types to replace lost or damaged tissues.
In complex organisms,the body organization is highly specialized and differentiated,meaning cells have lost their ability to revert to an undifferentiated state.
Therefore,only organisms with a simple body organization and the presence of these specialized regenerative cells can exhibit the phenomenon of regeneration.