Whenever someone posted a new commend, a static HTML file would get generated
It's essentially still a cache, with the same concerns/issues - mainly cache invalidation - as a HTTP cache.
An on-disk cache of that sort has other issues though. For example, what if a request is received whilst the file is being written? Does the system deliver a half-written HTML page? You can introduce locking or atomic file operations (write to a temporary directory, then mv the file into the correct location: mv is an atomic operation), but this adds more complexity to the cache logic.
One of the benefits of a HTTP cache is that they generally have a default graceful failure mode: if the cached data doesn't exist, request it from the backend application server.
