probably safety issues are a factor, it would be hard to get every one off if something happened at a station. But also it probably wouldn't get you much benefit over having two trains. The main advantage would be the back half would theoretically be able to load unload a little faster then if it was a second train waiting to come into the station, but with the downside that now the front half of the train needs to wait for the back half to unload and load before it can go on it's way
probably safety issues are a factor, it would be hard to get every one off if something happened at a station. But also it probably wouldn't get you much benefit over having two trains. The main advantage would be the back half would theoretically be able to load unload a little faster then if it was a second train waiting to come into the station, but with the downside that now the front half of the train needs to wait for the back half to unload and load before it can go on it's way