There is an actual reason why titans "eat" humans. You know how the Titan Shifter ability is passed down generation to generation by injecting the inheritant with a fluid made up of a human's spinal fluid into a person turning them into a mindless Titan and they consume the Titan Shifter thus gaining their powers and memories? The reason Titans eat humans is because they want to escape being a Titan, suggesting that they may have some sort of awareness. They eat humans in the hope that one of them will be a Titan Shifter so that they may return to their human form. Although the chance of the humans that they eat is a Titan Shifter is extremely rare, it has happened in the past. When Ymir was in her mindless Titan form, wandering the desolate lands of Paradis for sixty years before coming across humans; she attacked Bertholt and Reiner when they were younger and ate their friend who was a Titan Shifter, thus explaining how she became a human once again.