The conclave were built thousands of years before this picture is set when they were required to defeat the greatest enemy human kind had ever faced. At this stage, they thought they had failed. In their last attack they were mostly destroyed along with the vast majority of the human population of earth. 12 conclave units were still salvagable after the defeat, however their genetic structure was irreperable. They managed to salvage their physical properties by using genetic material from various feline species that they had stored in an archive of all the species of life destroyed during the war (The Ark Database).

Which is why they now look like big mean cat-people.