When you see good language use in writing it communicates its own sense of quality. This differentiates low-value sources where some people communicate without an appreciation of the minutiae of the language.

Now for forum comments or low-value writing it's not an issue, but you can argue that having someone who is experienced with using a style guide and communicating consistently adds some authoritativeness to the publications.

In the case of Wikipedia that is a valid thing to aim for.