It is when it is a multiple shunt, there is no access from the main line to Platform 1, you would need to cross over to platform 2, reverse, shunt into the Down Goods Loop, reverse, shunt back into platform 3 and reverse. As well as transferring the staff for the branch. The connection to the branch from the Down Goods Loop is also a ground frame.
By the time you did all that, you could have arrived at Stourbridge, got off the train, changed platform, got on the shuttle, arrived at Stourbridge Town and probably have got back to Stourbridge Jn if you wanted.
It is a faff, and a massive one at that. A curve would be prohibitively expensive considering the track and signal work needed for something that works perfectly well now.
It is the same as I have already asked, how many tram/trains are you expecting to go to Stourbridge? It isn't awash with capacity to turn trains around at.