As seen in the video game death stranding.
Two extinction level events happened and wiped out half of all human life. Building and cars and homes were destroyed and replaced by growling grass or dirt. A new species of bug came about called a cryptobite and a bridge was formed between the world of living and dead and hence forth came the rise of beached things
Genetic Engineering. They are changing the genes of something (In this case, Cabbage) to help is survive its environment better.
