I suspect that:

1 He wants to focus those on board to the task at hand. If there's no hope of help then the only thing they can do is kill the shark.

or

2 It's basically a macho thing that says 'I don't need anyones help'. After all Quint is a loner who basically doesn't ask for help and expects none.

Whichever way, the story would not have been so good if the whole town had turned out to help !

I suspect that it is due to one of the following:

1. He wants to focus those on board to the task at hand. If there's no hope of help then the only thing they can do is kill the shark.
2. It's basically a macho thing that says 'I don't need anyone's help'. After all Quint is a loner who basically doesn't ask for help and expects none.

Whichever way, the story would not have been so good if the whole town had turned out to help !

I suspect that:

1. He wants to focus those on board to the task at hand. If there's no hope of help then the only thing they can do is kill the shark.

or

2. It's basically a macho thing that says 'I don't need anyones help'. After all Quint is a loner who basically doesn't ask for help and expects none.

Whichever way, the story would not have been so good if the whole town had turned out to help !

I suspect that:

1 He wants to focus those on board to the task at hand. If there's no hope of help then the only thing they can do is kill the shark.

or

2 It's basically a macho thing that says 'I don't need anyones help'. After all Quint is a loner who basically doesn't ask for help and expects none.

Whichever way, the story would not have been so good if the whole town had turned out to help !