I shall try to make you understand. First of all we should understand, Allah our Creator knows a lot of things we do not know. So Him choosing a place will have its own wisdom. Also have in mind if the blessed location was in SA or China, then people would have asked why isn't it in India or Africa. Now lets try to understand the wisdom of Arabia being the location of Prophet Muhammad . First of all we should try to understand the condition of Arabia before the Prophet . Arabia was just a barren desert with no natural resources to sustain a great civilization. If we look into the history, in those times great civilizations were usually settled around rivers or places with a lot of natural resouces, life fertile land etc. During those times Persians and the Romans were the dominant two civilizations. It is said that Alexander reached the boundaries of Arabia and said, there is no use in conquering this land and he went back. Such was the deplorable state of Arabia. It was basically secluded from world civilization. The whole world never expected anything good to come out of this piece of desert. On a side note one should take note on the level of the language of Arabic among the people there. Even though most of the people couldn't read or write, Arabic was almost at its peak at that time. Because the lack of influence from other cultures and sparse immigrants. The language of Arabic was in a highly refined mode. Now Lets look at how the rest of the world were looking at Arabia. Suddenly in a span of 23 years a Man claiming to be a Prophet has suddenly united the Arabs and preaching a religion which people are accepting in the masses with a Holy book called Quran. He is said to be surrounded by Companions who are steadfast and people of justice. Even after His death the religion is gaining momentum. Now suddenly these companions and the followers of this Religion has reached the borders of Arabia challenging the Romans and the Persians. Within a few years they defeat both this empires. Their soldiers say 'We love the life of the Hereafter as you love this world', they have no fear of death. Suddenly Islamic scholars pop up in thousands and spreading across the world. All this is History, Just Imagine if African tribals from Madagascar in Africa suddenly spreads across the world defeating America, Russia and China. People would call it a 'miracle' wouldn't they? It is exactly what Happened with Arabia. Arabs were considered 'uncivilized' and primitive by the rest of the World before the coming of the Prophet . It is Allah's wisdom that He let his mercy come out from such a barren and unforgiving land.