Have you ever calculated the takeoff performance for a jet for a 4646ft runway (EIS) compared to multiple 8600-13,000ft runways (MIA)? Some major factors that can negatively contribute to aircraft take off performance are its hot, heavy airplane, high altitude, high humidity, and others, as well as the wind not being right down the runway (headwind improves performance and shortens the takeoff roll). Having up to 13,016ft of available runway in Miami is very different than 4646ft in the BVi.

As a pilot for 39 yrs (11 US Navy, 30yrs at my airline and current B777 Capt/instructor/evaluator), I’m glad they are cautious. Of course, YMMV. 😉