Answer:
The best answer to this question would be, that the reason is that theorists have varying views on the source of human intelligence, as well as how it develops, when it develops, and what are the causes for the development of human intelligence, as well as what stimulates it.
Although generally most people believe that intelligence comes from having a brain, and thus some believe that it has a genetic, or biological component to it, the truth is that although organically this may be true, intelligence cannot be simply explained through biology and genetics.
Theorists have thus focused on research about when, how, and why intelligence forms in human beings and what causes this, and drives this. Also, researchers have observed that different people may display different types of intelligence, instead of just one kind, something that cannot be explained simply through biology, or genetics, as basically all humans have the same organ.
Thus, researchers have gone on to focus on the causes of the development of intelligence, the sources of development, and what characterizes the different types of human intelligence.
