Iframes have a pretty bad UX and are ugly and difficult/impossible to properly integrate in any decent design. Also it does not work well with touchscreen and r

Iframes have a pretty bad UX and are ugly and difficult/impossible to properly integrate in any decent design. Also it does not work well with touchscreen and responsive designs. SSI nowadays requires a host with a specific server stack and configuration. Meanwhile, with purely static files it's easy to find high quality hosts or CDNs, even for free. For simple sites, it's much easier to pre-generate the static content and then upload the output files (Web 1.0), rather than dynamically generate it for every HTTP request sent to the server (Web 2.0).