A lot of times in this instance it comes down to chemistry. As bad as Alexandra is maybe she and the cat playing Luke didn't have the same chemistry or had none at all. You can't just go with "yeah she's cute so let's cast her" if your core responsibility is to portray this relationship it has to look real and if two people have no chemistry the show fails instantly
This. Chemistry is more important and vital than "aesthetics". To me, watching two people interact who have 0 chem is about as entertaining and exciting as watching a brick wall. Hearing that Ritter works well with Cage's actor makes me more excited for the series.