A prison in decline?

I just Googled 'Knaphill Prison' and came across this interesting record which suggests that the prison was almost entirely unoccupied by 1888. Huh, I wonder why? I also like how they use the term Convalescent Prison. I'm not quite sure the prisoners would have agreed scrubbing frozen bricks in the bleak mid winter.

PRISONS (ENGLAND AND WALES)—KNAPHILL PRISON.
HC Deb [sic] 16 November 1888 vol 330 c1384 1384

MR. HANKEY (Surrey, Chertsey) asked the Secretary of State for War, Whether his attention has been directed to the present condition of the prison at Knaphill, Woking, which is now almost entirely unoccupied; and, whether, in view of the great want of suitable barrack accommodation at present existing throughout the country, he will at once take such steps as will enable him to convert the prison into barracks, or utilize it for the military service of the country?

THE SECRETARY OF STATE (Mr. E. STANHOPE) (Lincolnshire, Horncastle) Communications have been entered into with the Home Office with a view of obtaining for military purposes the buildings and lands of the Woking Convalescent Convict Prison; but no decision has yet been arrived at. The position of these buildings, within easy reach of Aldershot, makes it most desirable to obtain them.