You misunderstand, the optimal amount of "loss" both internal and external, from Apple's perspective, is greater then zero. They know they could do straight forward things to reduce it, like put everything in the back room so you have to ask for it, or hire security guards to physically prevent theft.
But they decided that would be worse for business to prevent all theft then to simply have a few people steal stuff.
It being easy for people to grab thousands of dollars worth of stuff and run out of the store is a choice they made intentionally.
