Implementing caching servers and horizontal scaling is complicated and requires talented people who typically need to be on call. It's lot of complicated moving

Implementing caching servers and horizontal scaling is complicated and requires talented people who typically need to be on call. It's lot of complicated moving parts, which can easily go wrong outside office hours when a site unexpectedly gets popular. Where as with a static site, the complicated bit is only in the updates. A single server can handle massive numbers of requests and it's easy to scale further with a CDN.