"The Waterloo and City Line is closed. The Bakerloo, District, Hammersmith and City, Jubilee and Metropolitan Lines are partially closed. The Circle Line is partially suspended. All other lines* are operating a good service."
Well...there can only be one reason: BANK HOLIDAY!
*: That is Central (woohoo), East London (well no...because it is closed anyways), Northern, Piccadilly, Victoria, Overground and DLR