It's a Branch track , so what goes in has to come out before another train can enter... All terminals have this issue which you can see at Hoboken on the PATH or LRT during rush hour. The original proposal during the 90s would have created a loop track, but that would have torn up more of the wetlands. There would have been electrification as well and high capacity trains piggybacking off an MTA Metro North order, but that plan was scrapped and along with most of the 90s/early 2000s plan for the state which would have addressed most of the issues that come up today whether it's crowd issues at events in the Meadowlands or Newark or NY or daily commuter frustrations or the congested strained corridors.