Discomfort is the name of the game. When you are a prisoner, you have no control over anything. Food, water, sleep, work, warm, cold, clean, dirty, your surroundings, entertainment, contact with others, etc. Every aspect of your existance is the subject of someone elses whim.
Try going to sleep in your cell when the guards are blasting a tape of tortured sounded moaning and screeching. You can slump over all you like, but you won't get to sleep until your body is exhausted.
When you're a prisoner, you do what you're told, or they go for your comforts. Sitting at your keyboard, it's hard to have an appreciation of having no comforts, but the world revolves around them.
Why get your daily 'shower' in freezing water instead of warm? Why settle for two and a half hours of sleep when you could get five? Why eat rice when you could get some dessert? Why sleep on the floor when you could get a cot? Why scrub septic tanks when I could watch a movie?
Why not just sit in the stress position and answer a few questions?
The idea is to make people cooperate. Without any ability to influence people's comfort, anyone can hold out against interrogation. If the only tools you have to work with is asking the question again, then the person is free to ignore you until you get tired of asking.
It's not about beating people, it's about wearing them down mentally and physically by making them uncomfortable. Without the ability to make people uncomfortable, they simply won't break, and you won't get any worthwhile intel. This is what is going on now that our interrogators have been defanged.
I can sleep in pretty much any conditions, with any background noise, if I am tired and overdue for it. And I can stand freezing showers, lack of entertainment, and cold meals too. Although I have no idea whether I could resist actual torture (infliction of physical pain), I am certain that if all the enemy could do to me was what you describe, I'd never "break"; nor, I expect, would most combatants who had been well-trained.
I wouldn't even break under Abu Ghraib style "torture", which goes further than what you describe. Physical pain or threats to my family are the only things I'm not sure I could hold up under.