Again, it's inside an HTML code block. Not sure if there's a way to make it work inside that block?
#+BEGIN_HTML
...
<div class="page-header">
<h1>{{{title}}}</h1>
</div>
...
#+END_HTML
> {{{title}}} should do it. See
>
> (info "(org) Macro replacement")
Actually, I'm not sure it will do: macro replacement takes place during
export, so it may or may not be enough, depending on what you really
want to do.