Why are guyana suriname and french guiana all separate countries

The Guianas is a South American region. It includes the independent nations of Guyana, French Guiana, and Suriname (termed before as Surinen).
Suriname was received by the Dutch, from England, in exchange for "Nieuw Amsterdam" (at present,called New York).

French Guiana became a French distinct part overseas in 1946 , while Suriname  went through constitutional reform in 1948–1951 and was given  self-government by the Netherlands in the year 1954 and independence in the year 1975.
British Guiana on the other hand was then granted its own constitution in 1953. In 1966 the later also achieved independence as Guyana .