If Floyd Bennett Field failed due to its remoteness and isolation, how has JFK been so successful?
If remoteness killed Floyd Bennett, why hasn’t it killed JFK?
  


Because remoteness did not kill Bennett.

The opening of LaGuardia airport in 1939 absorbed all the traffic, then in 1941 the Navy took over Bennett and banned all commercial and GA flights. After WWII it was meant to return to commercial service to handle the excess traffic from LaGuardia.

(Idlewild was still being built – bigger land area, longer-runways potential, hints of the jet-age in the air, etc.)

But the Port Authority and the Navy could not agree on the cost of moving the Navy's facilities.


  The controversy between the Port Authority and the Navy that has kept commercial traffic out of Floyd Bennett Field in Brooklyn narrowed down yesterday to a \$450,000 question of price. The Navy is asking \$1,200,000 to transfer its facilities and the Port Authority is standing by its statement that it could not spend more than \$750,000 for that purpose. (nytimes.com, 1947)




Further reading: https://en.wikipedia.org/wiki/Floyd_Bennett_Field#History