Bhagwan Vishnu does not incarnate only to resemble humans because he assumes that form which is appropriate to the purpose of the avatāra.
We need to understand that what we call God, it’s not a human being but the Supreme Energy depicted in various forms.
So that divine energy which is pervasive and known as “Vishnu”, it can manifest itself in any form as and when needed. There is no such rule that the divine shall be in the form only a human.
He manifested in the form of Matsya, the fish since he had to save the creation from the massive cosmic flood. Since flood is related to water 🌊, he manifested as the divine fish.
Then when the Asura Hiranyakshyap attained the boon from Brahma that he neither by any human/man nor by any animal/beast, Neither during the day nor at night (specifically circumvented at twilight/dusk), Neither indoors nor outdoors (circumvented on a threshold/porch step). Neither on earth/ground nor in the sky/space. By no weapon forged or any living/non-living object. Since these all conditions were the part of boon, the asura was immune to death from all those factors. So upon identifying the loophole in the asura’s boon from Brahma, Vishnu assumes the form of Narasimha which was half man half lion and he picked those minute conditions which Hiranyakshipu couldn't mention in his boon and then slayed the evil asura and saved his devotee Prahlad.
So him taking the form of an animal isn't something unusual as the divine is pervasive not just present only in humans.
Then of course, Narayan as Shri Ram the ideal man (Maryada Purushottam) is one of the most worshipped forms of him.
And Shri Krishna, a very very popular form of Narayan.
So the human like forms of him are the most popular ones, but the animal like forms too had a lot of significance in his aim of sustaining the creation, restoring the balance of nature and protecting the world.
नमो नारायण 🙏