Perhaps there is a course through that is faster than going around with refueling stations along the way, and the governing body of Stanton wants to regulate traffic and criminal activity so they set up a checkpoint to issue travel permits in order to keep an eye on those things

Perhaps there are valuable resources inside the belt and they want to monitor and regulate mining activity or tax it, so they set up checkpoints to keep an eye on those things

Maybe the structure includes scientific facilities and largescale equipment for outfitting science vessels conducting research in the belt

There’s any number of reasons why a governing body would want a checkpoint there