My hunch on that is it might not need to be selected for, cells having largely the same features. Most animals don't live as long, so they have less time to dev

My hunch on that is it might not need to be selected for, cells having largely the same features. Most animals don't live as long, so they have less time to develop cancers. (Plants and fungi of course get cancers as well but the cells are immobile avoiding metastasis and they don't have single points of failure like organs.) But it's just a hunch.