Why were merchants in Mecca hostile to Muhammad?

Answer 1

Merchants in Mecca were worried that if the people of Mecca believed that there was only one god (Allah), that they would destroy the 'pagan' idols that attracted so many visitors (essentially, tourists). The merchants made the majority of their money off of the travelers that came to see the idols, and if they were destroyed, the merchants would have to find new ways to make money.

Answer 2

Merchants in Mecca objected to Mohammed on several grounds.

Preserving Religious Plurality: Meccan Merchants 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 these merchants did not take into account is that nearly all Arabians would convert to Islam after the fall of Mecca.

Attacks on Meccan 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 this directly affected the Meccan Merchants' bottom line, this raised enmity.

Polytheism: Many Meccan Merchants ascribed to various Arabian henotheistic religions and knew that Mohammed would demand that they abandon all gods but Allah. They did not wish to be forced to change their religion.