Is there anything I'm missing here? It makes so much more sense, especially with the NJCL during the Summer months. Someone told me that the Rahway rockets originate in South Amboy (hence why they're designated as NJCL trains), so it's definitely feasible to extend it. Really frustrating that they cant figure this out.
Well, I'm pretty sure everyone else has told you what you're missing. However, I will add a few more things. The Rahway Rockets (when they actually operate) do not originate in South Amboy. They originate in NYP and turn between Union and Graw Interlockings, just outside of Rahway. Extending it may cause it miss the returning, single track slot as mentioned by Andrewjw and would defeat the purpose of being a relief valve for the packed trains that run behind it.
The same goes for the Raritan trains to Hoboken. Not unlike a lot of the operation, the Raritan crews and equipment often tight turn on weekends. Sending them to Hoboken where they would have to long turn ( which is why it was every other train since it would not make it back for the next train) causes gaps in service, increased operating expenses, lessened operational flexibility and probably didn't yield the ridership to make all of this worth it.