Behind the scenes at South Kensington tube station’s escalator replacement project

Deep underneath South Kensington tube station, a huge project is underway to replace all five of the station’s escalators, and all of them at the same time.
To do that though, Piccadilly line trains have had to stop calling at South Kensington station and won’t call there again until next spring. Now, normally when escalators need replacing they don’t have to close part of the station, so why was this necessary at South Kensington?
It helps to understand a little bit about the