I'm not an employee, but based on the length, number of stops, and ridership (both the people who ride and the number of people who ride -- especially outside of Brooklyn), I think I have an idea.
Any sort of Lower Montauk reactivation would need to have a large shift in alignment, thereby only applying to a portion of the line. Something could be worked out for LIC, but the line would ultimately need to serve Manhattan and pass through less of the industrial area split between Brooklyn and Queens. (This goes for the subway and railroad sections.)