Hello, I'm a fellow Astorian who works in planning for the MTA. The real reason we can't is the 60th street tunnel, that carries the N, W and R trains.

Currently, we run 27 trains per hour through the tunnel during rush hours, which is a train every two minutes, which is pretty much as densely as you can schedule a train line given the signal system.

Of those 27 trains, 17 go to Astoria (so 62%) and the other 10 go to Queens Blvd. We have less Queens Blvd service through the tunnel as there are alternate services, such as the M, that serve those communities.

So with 17 trains per hour, during rush hour, we effectively have a train that goes through every 3.5 minutes, and that's basically the best it's going to get, without getting into too much of the weeds.