It's a design feature intended to prevent them from acquiring human normality. As an aside, Brendans are fairly easy to detect using the variant VKB test:

[Begin Transcript]

Interviewer (calm voice): You are walking along a beach when you encounter a huge robotic millipede. A human head is connected to each segment...

Subject: That's a bloody brilliant idea! Just imagine how rude cybernetic millipedes could be...

Interviewer presses "Rogue Brendan" button. VKB Test terminates.

[End Transcript]