I think the reason why kemono art is considered more aesthetically pleasing than furry art is because kemono art simplifies animal attributes as much as possible in order to maintain a mostly human appearance, whereas furry art operates in the opposite way, adding as many animal attributes as possible, even if it's necessary to change the base human form.
In most kemono art, the characters are essentially human with superficial modifications to give them an animal appearance. Ears and tail similar to the animal they are based on (often fluffier than normal), button nose and human mouth instead of a snout, small pads on hands and feet in reference to an animal's feet, and a uniform coat of fur that at first glance appears to be skin of a different colour are usually all the animal characteristics of a kemono character. Everything else remains human-like, including the character's behaviour, which rarely exhibits elements of an animal and is predominantly "normal".
Furry characters, on the other hand, try to be more faithful (as far as the base humanoid form allows) to the animals they are inspired by. The skull and face is almost identical to that of the animal (except for the eyes, which are larger to allow for a greater degree of expressiveness), the shape and distribution of the fur is designed according to that of the animal (areas with more or less coverage and different colours and patterns), the hands acquire details such as larger pads and claws, the shape of the legs and feet are altered to be closer to the legs of an animal, the shape and function of the genitals are designed based on those of an animal, and so on. The changes are so many that even the behaviour of the character is modified taking into account the instincts and limitations of the animal on which it was based, such as the way they dress, what they find attractive in others, the presence of the fetish of the artis, difficulty in using human tools, among other things.
It's this notable difference in the amount of animal characteristics that determines the degree to which the average person feels attraction or repulsion towards the character. Kemono characters, being mostly humanoid and having relatively few animal characteristics, show a much lower degree of repulsion than furry characters and a lower chance to fall in the "uncanny valley" because the characters often are humanoid enough to be recognized by the human viewer as entities similar to him or her. In addition to that, kemono characters usually have features such as eyes, ears and tails exaggerated to resemble those of an infant (human and animal), which triggers the protective instincts of the observer, raising the level of attraction to the kemono character.
Furry characters, on the other hand, tend to often fall into the "uncanny valley" because the large number of biologically accurate animal characteristics cover the humanoid base to the point where it is difficult to recognise it as an entity resembling that of the person viewing the character. In addition to the "unsettling" appearance, furry characters also often exhibit behaviours that can be "strange" and are accentuated by their creators' own behaviour, who often use their creations to express intimate desires rather than to capture the attention of other people.
In short, kemono are *pretty* human(oid)s with surface animal traits and "normal" behavior that doesn't intimidate real people, while furries are animals attempting to be human-like primarily for the sake of their creators.
Pic related, a comparison between kemono and furry characters designed using the same template and base animal, plus a template in case you want to mess with the designs.