Why do you think everybody is too busy to come take care
of Gatsby's situation after his death when they add all the
time in the world to come to his parties

after Gatsby died, his status had been already tarnished. He was no longer the greatly admired and respected man in those peoples' eyes. he was a suspect of murder, he manipulated some people, and even though he may have achieved his lifelong dreams, he was merely a dead man and nothing more. everyone practically realized that, prompting them to not care for Gatsby.

hope this helped!!

Biology affects behavior also through mechanisms of heredity regulated by genetic principles. The nature versus nurture controversy— that is, how much of our behavior is due to inherited factors and how much to environmental factors—is a question that has plagued scientists for years and is still unresolved.