Are you sure? Aren't they just trying to show the most appropriate pets to the most appropriate people in order to make adoptions quicker? Where do you read the euthanization part?
Unfortunately, most pet shelters get more pets than their facilities are able to handle. Unless they're a no-kill shelter (in order to be considered one they need to kill <10%), they will need to euthanize in order to make room for incoming animals. This is as opposed to promoting adoption, fostering, etc. An algorithm that can prematurely decide what animals will be adopted, or have the best chance to be, can create a perverse incentive to euthanize early the less optimal pets.