Idol were not worshipped by Arabs only in the seventh century, but also in India, Greece, South America, China, Japan etc while the Prophets and Scriptures were sent to the Arabs only. Why?
It appears that God's design for spreading His word after the coming of the Prophet Ibrahim (pbuh) was to use a specific nation as the chosen nation and to leave the responsibility of spreading His word on this nation. (Our understanding is that before this era, the Almighty would sent prophets to different nations as appropriate.)
We understand from the Qur'an (as it is also evident in Torah) that the first nation that was chosen was Bani Israel. We also understand from the Qur'an that the Almighty then chose Bani Ishmael (that are most Arabs living in Arabia at the time of the Prophet) to spread His world.
If you think about it you will find that both nations at the time were living in a point on the face of the earth that could be considered as the central point or near the central point from the economical and political point of view. This of course was not the only reason for choosing these nations but it certainly makes much sense.
It was the result of this selection that Islam spread to the west and the east. Today the total percentage of non-Arab Muslims (Indonesia, Pakistan, Iran, ...) is far greater than the total percentage of Arab Muslims. This was all due to spreading Islam by the chosen nation of God who lived at the right place of the world (for this purpose).
No doubt, if the chosen nation of God (Bani Ishmael) had not done the similar mistakes as the previous nation (Bani Israel) and had chosen to remain collectively obedient to God's religion then we would have seen a wider spread of Islam in a peaceful manner