Not quite true, Webmentions are used extensively by the IndieWeb[0] community (which is where the Webmention spec was born).

It's unfortunate that the author linked to the Wikipedia page instead of the Webmention page on IndieWeb wiki[1], which I'd argue is the canonical point of reference, since it has a lot more information and various examples.

It's arguably a niche feature used by a niche community, but it doesn't have to stay that way! Adding Webmention support to your website is actually quite easy since there are free hosted services[2] that let you receive Webmentions to any URL on your (static) site without having to run any code yourself.

[0]: https://indieweb.org [1]: https://indieweb.org/Webmention [2]: https://webmention.io