Why did the leaders of Mecca begin persecuting Muhammad and his followers?

While the Muslims lived in Mecca, the Muslims adamantly demanded that the population abandon their henotheistic and polytheistic religions and openly threatened to destroy their idols as God had told him to do. Understandably, this angered the Meccans greatly because their religions were special to them and they took to violently beating Mohammed and the Muslims to prevent them from destroying their sacred objects.

Once Mohammed and the Muslims left Mecca, Meccans no longer feared these negative outcomes and had little reason to continue to care about a small minority like the Muslims. However, while in Medina, Mohammed coordinated numerous raids on caravan shipments that were lightly armed and not antagonistic. At the time, Mohammed and the Muslims needed supplies in Medina and did not have the funds to buy such supplies on the open market. As a result, he resorted to violence to achieve his objectives. This persistent action (of violently attacking merchants trafficking through Arabia) caught the attention of the Meccans whose commerce he was ruining. This resulted in the Ghawazat (غوزات) or Skirmishes between Meccans and Medinans.