Seems like a lot of work and money for a small gain in territory. The Antonine Wall was much better placed.
It was probably temporary, and originally viewed as an interim step in full conquest. The trouble wasn't that the people couldn't be handled -- a comical claim one finds a lot on the web -- it was that there wasn't much of any value there. The Antonine Wall was occupied twice; the problem both times was that the territory in between wasn't attractive to the Romans, and didn't have much appeal to the conquered populations who provided auxiliaries to the legions. Starting no later than the 2nd century AD, Roman cavalry in Britain was drawn from the Sarmatians, who were beaten by the Romans and integrated into auxiliaries (moved to an area where they were considered foreigners and enemies, and without prospects of returning to their homeland).
If Mons Graupius was nearby, it might explain it’s position - an “in your face” statement.