> because people don't know how to do it efficiently
Of course we do.
We just choose not to bother because delivering features efficiently is often more valuable than shaving off a few seconds of download time. Especially when it's typically once off and then cached.
Apparently not. A few seconds is a really big deal, but that is just download time while you are also clearly not accounting for execution time. Caching code will not save on execution time.
