Why are countries such as Belize Guyana and Suriname considered part of the Caribbean?

Belize and Guyana as former British colonies and Suriname as a former Dutch colony have many cultural ties to islands [the West Indies] colonized by the British and Dutch in the Caribbean Sea. The Caribbean Sea washes upon Belize's coastline.

All three countries belong to the economic organization Caribbean Community [CARICOM]. CARICOM's headquarters are in Georgetown, Guyana. All three countries also belong to the Association of Caribbean States [ACS]. The ACS emphasizes the Caribbean region to promote cooperation in natural disasters, tourism, trade, and transport.