I am specifically complaining about WordPress. Anyone could make a server side dynamic application that applies proper caching headers to work with a CDN. Anyone could, but WordPress specifically did not. It's an uncacheable mess by default and caching plugins just barely make it useable.
Using a static site generator is basically just a way of ensuring that the pages are properly cached by the brute fact that they've been dumped out on disk. It's not strictly necessary for a well designed system, but it raises the floor because even in the worst case, the pages are static files.
For many public facing sites, dynamic applications aren't strictly necessary. If you're just hosting a PDF of an Excel spreadsheet of permitted job categories, you don't need a dynamic application. Again, a well designed app would already be hosting this through S3, but you can't trust things to be well designed when made by a contractor with no technical oversight.
Static files don't automatically set any headers either, you still need a webserver to serve those. And you can override those headers in the server or in the CDN so there's no reason to switch out the entire backend for it.
CDNs handle scaling of static assets. That's their entire purpose, with features like request coalescing and origin shielding to help ensure unique URLs are never requested more than once. Optimizing for static files at the origin is just not worth the trouble when Wordpress and other frameworks are far more productive and provide CMS functionality which is usually needed anyway.
We're talking in circles. No one disputes that CDNs are good and expert users of WordPress are capable of making it not shit the bed. The point is that WP cannot be left unmanaged by novices, which means it should not be used in many situations in which it is currently used. Static sites have a higher floor and so are better suited to non-expert use.
My point is that tradeoff isn't worth it. It's far easier to tweak security settings and configure a CDN than to completely change the backend with a complex build process requiring more technical knowledge, deploy it to a host which you still need, configure a CDN which you still need, and wire it up to read from a CMS which you still need.
Using a static site generator is basically just a way of ensuring that the pages are properly cached by the brute fact that they've been dumped out on disk. It's not strictly necessary for a well designed system, but it raises the floor because even in the worst case, the pages are static files.
For many public facing sites, dynamic applications aren't strictly necessary. If you're just hosting a PDF of an Excel spreadsheet of permitted job categories, you don't need a dynamic application. Again, a well designed app would already be hosting this through S3, but you can't trust things to be well designed when made by a contractor with no technical oversight.