Another good reason for odd connections is that it's easier to guide people on common routes. For example, around Bank and Monument, it's often quicker to walk above ground - but only if you already know the route. If you're a tourist, you're herded underground with very clear signs.

It's like progressive disclosure in software. By requiring some level of expertise even to see the options, you help to ensure that novices can't accidentally break things (in theory, at least). Imagine what would happen if TfL did this explicitly with signs saying:

<-- Quick route that way :: Easy route that way -->

They're making the decision for you, assuming that if you're not sure, then you need the easy route.

Other examples of this in the physical world:

* The 'Black diamond' lane in airports (especially when they weren't advertised)

* Special unadvertised rates in hotels

* Theme parks with tickets for bypassing queues, though when these are advertised, they're more like price discrimination than progressive disclosure.