One of the main reason for this variety to be so wide is colonization. In the Caribbean there were mainly three types of colonies: English, French and Spanish. Also, on top of that, they brought slaves from Africa which help to add African culture to the mix, leading to a more profound exchange of cultures.
Taking that into account, it is normal that there is so much diversity. Traditional practices from every individual island mixed with the ones coming from their colonizers and their slaves, creating entirely different practices in every single island.