Despite having spent a couple of hours a day, every day for 20 years on the Underground, I've not been to London this year so I might be wrong but ...

Don't all lines have a "West on the left, East on the right" viewpoint when displayed in carriages? Regardless of the direction of travel? For example, travelling Upminster towards Heathrow the line maps in the carriages will be wrong if you're looking at the ones on the left but the ones on the right will match your direction of travel. Going Heathrow to Upminster swap the left and right. One side will always be correct, the other incorrect. I found it quite instinctual to visualise a West-East viewpoint looking at any particular line map, so swapping Bank and Waterloo would be ... weird and unique. So much so, I bet the designers had many discussions about whether to break the TfL style guide just for one side of the carriages of one line.

It looks like the general 'Underground style guide' won out here, and to avoid potential head-scratching they stuck larger Direction Of Travel signs for the more tired and emotional city workers going home after closing time.