Many small companies only need a handful of pages on their website.
Site Builders build these pages as HTML code.
So for small sites, the site-builder has the following advantages.
1. The site needs no CPU to complete so it's unlikely your site will slow down.
2. Your site will be faster than dynamic pages
3. If you haven't used stupid FTP or C'Panel passwords, its unlikely you will ever get hacked.
4. You won't need to learn a CMS or spend any time updating all the scripts every week.