One reason we keep it 11:11am is because it sparks interest and conversation just like your question and it's unique so it sticks in people's minds.
But way beyond that, and certainly more important, the time 11:11am was a special time between Founding Pastor Steve Berger and his son, Josiah, who transitioned to Heaven on his 19th birthday due to a tragic car accident. It seemed fitting to honor his legacy in this way.