For a constructed language using non-human forms of expression, you can check out Rikchik language, created by Denis M Moskowitz [0].
> No one is going to ever speak this language except the creator to himself.
Well, it’s a hobby and an art form. Do you ask someone drawing still life compositions, why he/she is doing this, when photography is a thing? Besides, people DO use the language in this particular example, although more as an interesting pastime activity than a regular language.
Granted, constructing languages makes an extremely niche hobby. Still, without it there probably wouldn’t be The Lord of the Rings (for Tolkien’s opinion on language creation, check [1]). There are still people learning Klingon, Lojban, toki pona, Dothraki, and so on.
Esperanto and modern Hebrew (to some extent) are also more practical examples of this art.
For a more elaborate insight into this hobby, there is the book “In the Land of Invented Languages” by Arika Okrent.
[0]: https://www.suberic.net/~dmm/rikchik/rikchik.html [1]: https://en.wikipedia.org/wiki/A_Secret_Vice