Post author dropdown doesn't show custom roles

I created a new role and gave it standard author capabilities. However, when I edit a post as the admin and try to chance the post’s author, users with the custom role don’t appear.

What am I doing wrong?

$capabilities = array('read'=>true,'edit_posts'=>true,'publish_posts'=>true,'edit_published_posts'=>true,'delete_posts'=>true,'delete_published_posts'=>true,'upload_files'=>true);
add_role('agent','Agent', $capabilities);

[ Please do not bump, it’s not permitted here. ]