How did the Malays convert from Hinduism/Buddhism to Islam?

I did some research in the topic and found that their source is from Muslim traders from Arabia and India around the earliest 11th century. It is not until 1405 where the Malacca Sultanate adopt the Islam religion and become a Muslim state.

I am curious how the rulers and people of Malay convert to Islam easily when they already have an established religion. That goes to Indonesia as well.