I answered this in another similar thread and it didn't go over well, but I'll try again here.
Humans relate to close-to-human things.
That's you answer. It's biology...or some such.
We see ourselves in EVERYTHING. We attach human sentiments to everything we come across.
Show the Lions as the 'humans' and the Gazelles as 'food' and we root for the Lions.
Show the Gazelles as the 'humans' (as in develop their story/personalities) and we see the Lions as animals.
We watch videos on YouTube of insects and someone says "That spider was like [insert human emotion, attitude and phrase]"
If you create a race that is (looking fully) inhuman, we will not relate. You will need to always add TONS of human personality to get, even the smallest attachment. The same goes for robots. You can do a lot with the personality to make a character out of something non-human.
Faces are important. We LEARN peoples' faces by how much they differ from our base expectation.
That is why people of another race always look similar until you build a library of their faces.
For any artist creating a strangely different race, you will have the challenge of making very similar aliens, but still have them differ from each other - enough to recognize the individuals.
Orcas have different spot patterns. Cheetah have different spots. To humans, they all look alike.
That's one more problem to deal with.
It would be wild to see the work of an alien artist depicting humans.
We would all be the same size, have the exact same face and haircut, but have different skin and hair color.