I agree its busier in the summer...but that's the point..its still really dark and I don't think a car parked at the side is really something anyone looks twice at...if that's how the SK dumped the bodies...from the side of the roadI agree. Whoever did this does not even have to have lived there at all.
It's hard to describe to someone without sounding contradictory what this area is like. Yes it's desolate. But it's also busy in the summer. And when the OBI was there, many people traveled Ocean Parkway just to get there.
So that's why I think the bodies found may not be from just one killer. Most LIers know what this area is like, not just the few who live/lived there.