Question

Why is studying human-environment interaction necessary to understand the economic geography of the Arabian Peninsula in the time of Muhammad?

Answer 1

Because economy within a certain region will be heavily depended on what resources that are available in that region.
Since the Arabian Pennisula do not possess a good climate to produce agricultural products, it's almost impossible for agricultural sector to flourish in this region, and therefore they focused their economy on things such as oil, silk, zaitun, etc.