Why do people differ in height?

Answer 1

People probably differ in height because of their genes. If your mum is tall and your dad is tall, then you are probably going to be tall and the other way round, if both of your parents of short you're probably going to be short too.

Answer 2

Human body height depends on many factors, mainly genetics, race, feeding habits/resources, diseases/impairments and the environment. Depending on the combination of these and other factors people will be taller or smaller than others.