Because its the law of averages with plants. To get to two flowering plants that are equal performers, you needed to start with 4 - 5 veg plants which started from 6 - 7 clones which started from 10 or so cuttings. At each stage you would have culled the week ones and continued with the strong. Eventually picking the two best performers for flower.

Instead one plant is stronger than the other and is shouting to the other plant, "I drink your milk shake! I drink it up!"