Making people give up sleep is a traditional method of reducing their intelligence, so they are less likely to see through the bullshit or design an escape plan. Every decent cult does this to their new members.

But reducing their attention by uncomfortable clothes -- that's subtle!

Either way, seems to me this is not about pleasure per se, but rather about reducing mental abilities using unpleasant means. There are also pleasant things that reduce mental abilities, such as singing or praying together, though. It would be interesting to have data about how this correlates with the "ban on happiness" -- whether cultures opposed to happiness consistently oppose both "anti-system" and "pro-system" happiness, or whether the ban on "anti-social" happiness is used as a motivation to engage more in the "pro-system" happiness.