I'm just making a barely-educated guess, but I think the reasoning goes, the 'authorities' are the enemy. If in prison the currency is respect, yes you are disrespected if something of yours is stolen, but the "disproportionate response" of going to the authorities (read: the people who took your freedom) is orders of magnitude worse.

Prison isn't the most reasonable place. If the school bully steals your lunch money, your best bet is generally to stand up for yourself. After all, nobody likes a snitch.