TL;DR: Catholicism's large number of saints worshipped allowed polytheistic African religions an easier surface to graft on to. However, to reject the question: Syncretic religion existed and continues to exist in both former British possessions as well as the United States. Many elements of African religious tradition are now present throughout American religion and popular culture.
Long version: The ritual structures of Roman Catholic worship, particularly the reveration of a pantheon of saints, allowed easy transposition of West African orisha. These transpositions vary from region to region (Ogun, the warrior spirit and spirit of metalwork, for example, is associated with St. Peter in Santeria, St. James in Vodun, and St. George in Candomblé). According to Peter Williams church authorities in these regions were tolerant of this mixing of religions as long as church authority was respected.
I don't have a ton of information on British possessions, but there were certainly syncretic religions in Jamaica, with Kumina having perhaps the most purely African elements (Kumina ceremonies are most commonly related to funerals and births) and Rastafarianism being the most famous. We have a good bit of documentation of early African culture in Jamaica thanks to the prints of Isaac Mendes Belisario, a Spanish-Jamaican Jew. Belisario's existence and work suggests Jamaica had a fairly tolerant religious environment, as Jews were granted civil rights by the Jamaica Assembly's Jewish Emancipation Act in 1831. The significant 19th century population of Jews in Jamaica also helps to explain some of the syncretic origins of Ratafarianism.
It's perhaps telling that the one major inroad Afro-syncretic religion made in the United States was through the footprint of vodun in Catholic Louisiana, spreading into the Mississippi delta.
The evangelist nature of southern American protestantism also likely contributed to African religious traditions being absorbed into "legitimate" Christianities rather than syncretically mixed. Many of the symbolic gestures and forms of bodily expression seen in southern baptist church services, for example, can also be seen in Caribbean and South American festivals and other religious events, as well as in daily life in Cabinda, Angola, and the wider DRC.
(A tangent, because I'm currently watching a football game: Many of these religious and spiritual gestures have made their way more deeply into general American culture, particularly southern sporting culture. The cheerleader pompom stance with left hand on hip and right hand in air is a ward against evil. A symbol called "yangallala," an expression of transcendental joy in central African religion, and dated as early as ~8,000 years ago in northern Angolan cave paintings, is now used as the "touchdown" signal in American football. What I'm attempting, crudely, to say is that elements of African religion did not disappear entirely, they were simply mixed more broadly beyond religious culture.)
Williams, Peter. Popular Religion in America: Symbolic Change and the Modernization Process in Historical Perspective
Barnes, Sandra. Africa's Ogun: Old World and New
Martinez-Ruiz, Barbaro. Kongo Atlantic Body Language