This is a symptom of low road demand for Queens-Brooklyn transit which in turn is because of the relative size of both boroughs, their lower population density and most importantly because there isn't a subway line that truly cuts across the two boroughs.

If there were a proper subway line, running say from LGA, through Jackson Heights, Ridgewood and then cutting east through Brooklyn to JFK there's no way a driver could go faster on Grand Central Parkway anywhere near peak times.