Pre-rendered markup and assets are served directly from a CDN.
With no servers or databases to hack, common vulnerabilities are greatly reduced.
CUTTING COSTS / EASY SCALING
Hosting static files is cheap, and since there are no databases or servers, there's no need to handle load balancers, and the CDN can manage the scaling process.
BETTER DEVELOPMENT EXPERIENCE
Since the entire site content is static, it can be managed through version control. Tracking change history becomes more straightforward, and updating the site is as easy as uploading a new copy of the site and invalidating the cache.