A static site can't enable...
- User management (Members)
- On-site-comments (That Search engines can find)
- Voting (Polls & Ratings are very popular on Wordpress!)
- Carts (For selling products)
- Any user submitted content
...without 3rd party services that rely on JS.
This means that you rely on several external services for the site to have these features and in the end, the costs will be higher than running it on Wordpress.
But it could possibly be easier to maintain, be more secure, have higher performance and the dynamic parts wouldn't all fail at the same time so the uptime of the core site could be better.