If that is your starting assumption then, yes, they will never be sentient even when they will be. I am a neuroscientist. We do not know how the brain works and what causes an animal to be sentient. We do not know if a dog or a fruitfly are sentient in the way a human is. We know nothing about consciousness but you guys appear to be full of certainties about what can and cannot be self-aware.
Philosophical zombie is the term, incidentally.
It may be a non-complete duck that cannot fly, mate, feed, defend itself, react to surroundings and so on and so forth.
You are absolutely responding in a way which is appealing to the fitness function imposed on you - we all are. And that's the simple, very mechanistic one that's easy to point to.
like, if you and I chatted for 15 minutes intensely, i'd be pretty confident about what i think what you think of me (and vice versa for you) and if we're going really deep, if i'm trying to be really smart, I could also try to engineer what you think of me (which honestly is a daily occurrence when you are trying to make friends with someone, change someone's opinion, despite sounding devious)...
What constitutes belief in your view?
Irrefutable psuedo-facts.