Other animals might feel pain, but they don't know to the extent of resent not being in a more optimal state. — schopenhauer1
You are just throwing together many claims, some in which are inconsistent with others you've mentioned, without any form of source or evidence to support them. So I am not convinced simply by your words. I will also say animals do feel pain, not might - especially those have a fully functional nervous system.
https://www.nuffieldbioethics.org/wp-content/uploads/Animals-Chapter-4-The-Capacity-of-Animals-to-Experience-Pain-Distress-and-Suffering.pdf - as for the question of resentment that was still not stated in your OP, but you have since shifted the discussion from "dislike" to resentment - compelling evidence observed that some animals have a capacity to feel resentment and other complexities which refutes your claim otherwise. It seems that animals experience things with less persistence/duration, but still have the capacity and do experience complex emotion but lack the ability to ruminate or philosophize (at the highest current degree - humans) - which to my mind, is not a requirement to experience extreme dislike i.e., OP.
When you mention "optimal," state that alludes to morality and well-being. It has been observed that animals of higher degrees of consciousness (i.e., elephants, dolphins, chimps, maybe some dog breeds), have a capacity for morality, thus can comprehend a more "optimal" state of well-being, even if it is lesser than the optimal state of human standard.
https://www.livescience.com/24802-animals-have-morals-book.html This would be a response ingrained in homeostasis - humans function the same way; as a response because they no choice otherwise, not different from other animals. So then I pose the question: Do animals need to "know of homeostasis" to thrive and recognize the opposite of it is sub-optimal and puts them in a prolonged state of distress? Like humans, I will say no. And the "why" (in the form of existentialism) is not needed.
We've actively observed in behavioral studies of animals that certain species can feel clinical depression - to some extent suicidal depression, anxiety (i.e., separation anxiety - a sense of worry and longing) and other complexities. To my mind, the "optimal" state would be alleviating these anxieties and depressions in animals. But these are in animals with more complex degrees of consciousness. A human degree of consciousness and understanding is not necessarily required to experience complex emotions and altered mood states - but not having the capacity required to ponder or rationalize on the meaning of ones feelings (i.e., logic). But I don't think this itself is necessary to feel a prolonged state of dislike and dread for living/life - as seen in animals that suffer depression after separation from mates or broken bonds.
To then, this brings me back to my second and third paragraph: how much "logic" or ability to "do logic" or do animals have to RUMINATE - in order to experience or "want" an optimal state of well-being (to be a moral agent/moral being)? Certain species seem to have passed this threshold, and to deny this would be more of a categorical mistake if not a human error to evaluate animals - or compare them - to the degree of the human, or else they are not moral agents. Instead it seems like most of the humans "dread for life," comes from their thinking capacity, but this is distinct from other animals at lower levels of consciousness. Because there are no "moral facts," to which are only accessible to higher-degree beings as there are no moral facts - we can conclude that also humans do not require knowledge of 'moral facts' in fact - and then rationalizing them or using logical deduction (of ones feelings) to be considered a moral agent - or execute "morality" and no such knowledge is required. This should be (if we are to have intellectual integrity) consistent with animals.
In some degree, I mentioned this earlier about "exempt" humans that go through periods of disassociation or lapses in reality, altered states of consciousness, neurological disorders/damage, etc -- yet they are still viewed as moral agents with a capacity for higher order thinking in your previous post. All in all, your posts seem quite anthrocentric. So why this inconsistency other than a bias of some sort toward animals perceived to be as "lesser" than the human?
It does vary from animal species to animal species (e.g., elephant/dolphin vs rat/mice). In less complex animals, they may be possibly reacting to the pleasure and pain balance. We see this in humans as well. You may find this interesting:
https://neurosciencenews.com/pleasure-pain-brain-15367/