Grav is a tool to make « static » webpages. Wordpress is used for dynamic webpages (where users can log in, access some sections that, for example, not logged users can not access, etc.).
The main advantage of Grav (static web pages) is that it’s easy to have it in a code repository, like Gitlab/Github) and everybody can improve the website. That’s the way how Duniter wiki has been done, and that’s the reason you have a bottom right button to « Fix this page »: Wiki - Duniter
Another advantage about static web pages is the low maintenance costs, because they don’t need any database nor programming engine like Apache/Nginx, etc. Server requirements are lower too…
But I think a simple alternative to grab is Jekyll: https://jekyllrb.com/
In the other hand, static pages are harder to edit/collaborate for non-tech users. The opposite than Drupal/Wordpress dynamic sites.
Ps.: By the way, I could, if required, build a website using Jekyll (static) or Drupal (dynamic) and host it. I’m not talking about the « idea », contents, structure, just the « technical » stuff to let content managers, editors, etc. have a web to put the info there We can maintain the website just using donations, in an « open collective » way. That’s what we are doing at https://girala.net