Why did the wealthy clans of Mecca oppose Islam?

Answer 1

Preserving Religious Plurality: Abu Sufyan and the Meccan Leaders opposed Mohammed because the religious plurality permitted in Mecca was critical for maintaining Mecca's important position along the Arabian trade routes. It was on account of the fact that Mecca was holy site for all Arabian faiths that spared it from internal conflict and allowed the flourishing of commerce in the city. Mohammed made clear that he intended to purge the idols from the Kaaba which would cause mass uproar and ended Mecca's position as a holy site for all Arabians.

Of course, what Abu Sufyan and the Meccan Leaders did not take into account is that nearly all Arabians would convert to Islam after the fall of Mecca.

Keeping His Own Power: Abu Sufyan was one of the Chief Leaders of the Qoreish Tribe and one of the most powerful men in all of Arabia. Should Mecca fall to the Muslims, he would certainly lose substantial power. Many Muslims hold that he was corrupt as well, meaning that he stood to face criminal acts if he were subject to Mohammed's authority.

Protecting Commerce: During Mohammed's Medinan Period, Mohammed organized and executed numerous raids on caravans heading to and leaving from Mecca, causing disruption to Arabian trade routes. Since Abu Sufyan and the Meccan Leaders were in charge of Mecca, this was something they would be expected to ameliorate.

Polytheism: It was likely that Abu Sufyan and the Meccan Leaders were fighting in defense of Arabian henotheist religions to which they ascribed against Mohammed who would demand that he abandon all gods but Allah.