Kentucky Fried Chicken
The answer is that St. Vincent doesn't have any flat open areas that would easily support beef cattle, so there is no local tradition of eating beef; except for the plantocracy, who ate imported beef.
Nowadays you can get a hamburger, but there is no volume sales that would pay for a franchise; but there is a volume market for fried chicken. Chicken will manage to live as scavangers, so they're a protein source that has been traditional on Caribbean islands.
The Kentucky Fried Chicken process, which uses imported, grain-fed chicken, and pressurized deep fat firers, amounts to an upgraded local traditional food. It is both popular and expensive.
The visitor will find that chicken is widely available even in small food shops, but unless you eat in your hotel or a fancy restaurant, don't expect anything like a Big Mac.