Oh, that's a davit beam/arm. It's a crane.
I would guess it's for some some sort of access lifting requirement at the top of the lift hill. Possibly some sort of emergency situation - either to recover a train or passenger from the lower level catwalk after the crest, or more simply for lowering any of the larger lift hill components.
To answer the question "why is this not on every B&M" - I don't know. My two guesses are:
1. They can't get access for a mobile crane out to a suitable lifting location at the end of the pier (possibly ground stability or space issues), so this puts the loads through the already completely footers.
2. There's a local requirement in the Swedish regulations that asks for things like this. It's not uncommon to see them on industrial buildings in some countries (although they can be well hidden) and, whilst it's actually good building design, it's also sometimes mandated.