Websites can get complex...
You either embrace the complexity with a bespoke website design, or you abstract it away like the Site Builders do. In the case of the latter, the software lets you create pages without any knowledge of coding what so ever, but at the expense of what choice. You can ONLY do what the platform allows.
So you are sacrificing ability for ease. The same is true of the obverse of course; bespoke websites offer anything that is technically possible, but it's not something many business owners can create, let alone want to support.
The CMS route however tries, successfully we think, to operate in the sweet spot between the two. Offering greatly enhanced features, with speed of design and build.