Why did Lucretius reject the belief that souls migrate into new bodies?

Lucretius rejected the belief in the transmigration of souls because his atomic theory posited that the soul is a physical system composed of exceedingly fine atoms.1

According to his work De rerum natura, the soul is born and grows in conjunction with the body. Because it is a material system, it is inherently perishable; upon death, the soul's atoms are dissipated like "smoke," meaning it cannot survive to migrate into a new body. Lucretius explicitly opposed the views of Platonists and Pythagoreans, who taught the transmigration of immortal souls, as he viewed such doctrines as sources of irrational religious fear that prevented humans from achieving peace of mind. By demonstrating that the soul is mortal, Lucretius sought to liberate humanity from the fear of death and eternal punishment.1