Since June 2010, Apple has introduced custom chip design with its own names. In June, it introduced the A4 chip in iPhone 4. Since then, the company has been following a simple name pattern. I must admit though, the names can get a bit boring at times and not very easy to remember, and even Apple has realized that.
Confirmation coming directly from Apple, they told our friends over at The Verge that the A11 chips name received the Bionic name “because the company realized names like A8 and A9 weren't particularly exciting compared to its competitors chip names.”
Apple does have a point. Take Qualcomm's Snapdragon lineup. It's very easy to remember Qualcomm's Snapdragon chip line because it's snappy, simple, and easy to remember. If you think about Apple's own A-series chips, they are quite boring and not the easiest to remember.
Apple introducing Bionic for its new A11 chip is a good marketing move, but it's a marketing gimmick more than anything. Still though, there doesn't seem to be anything wrong with Apple's move here since it's just a name to remember the chip better. The chip's performance is not a marketing gimmick, however.