User blog comment:Beast of burden/BIOSHOCK 3: BIG BROTHER/@comment-6024608-20131019121029/@comment-6024608-20131020033600

They stated in the game that Little Brothers didnt work as ADAM processors (they could be conditioned NOT to eat the corpses (or even before the whole corpse 'gathering' thing, where Little SIsters were just farmed  to produce ADAM)   The Little Brothers didnt work out, so Fontaine didnt bother...

The Thinker thing is just an idea to justify why there would be Little Brothers  (why sea slugs would be used on them  - more than just the few in the initial ADAM production research tests which failed).

Another idea (like the Lockbox Gnomes) would be employing the Little Brothers to carry near-corpses back  to the Vita-Chamber machines (the teleport stuff and 'quantum' entaglement is just an advertising scam...)   You are unconscious and wake up in the machine after being healed, and the Little Brothers are back in hiding....