Shoreditch high street: completely enclosed?

I went through Shoreditch high street the other day, and it occurred to me that it's completely enclosed for no obvious reason. Looking on google maps, it looks as though they've enclosed the line for entire section between Brick Lane and the A10.

If, presumably, this is done so that a building could be built on the same land around the station, why would TfL have footed the bill for the enclosure? Surely this cost should fall on whoever's putting the building up?

I think the reason that the box was put up when the station was built. Was so that if the air rights are sold, then the building of that building will cause the least amount of disruption to the railway. For example if the box was built today, it would cause numerous possessions to fit it.