It's more to do with the standard library being so barren of common application needs, and looking for a solution that the community has gotten behind. Axios has been a common dependency in many codebases, because it is a solid solution that many have already used. Every developer could try building all the libraries that they would reach for themselves, but then each company has now taken on the task of ensuring their own (much larger) codebase is free from security issues, on top of taking care of their own issues and bugs.