A starship's brig isn't really suitable for the long-term holding of a prisoner. It's basically a slightly more advanced holding cell to what you get in modern police stations, and didn't offer Suder anything more than a bed and the most basic of hygiene facilities. They were there to hold someone until they could be handed over to the proper authorities. As he was effectively going to be a prisoner for the rest of his life, it was the sensible idea to place Suder in more comfortable quarters. He would be easier to manage and take less mangement if he had access to a proper bed, a bathroom and a replicator. The more ample space of living quarters gave him room to exercise and work on projects, and a window would help deal with the sense of claustrophobia you'd get staring at four walls in the brig.