I still use server side includes. It is absolutely the best ratio of templating power to attack surface. SSI basically hasn't changed in the last 20 years and is solid in apache, nginx, etc. You can avoid all the static site generator stuff and just write pure .html files.

It should not have gone away. It never did for me.

Also, this is kind of what 'frames' were and how they were used. Everything old is new again.