footer.html not being included on CentOS?

Question

I'm a part time Apache admin (but not by choice). I'm trying to get a common footer configured on CentOS 7. The pages are plain HTML and they are being served correctly, but they lack the footer. I have performed a apachectl restart several times.

Here's the configuration.

httpd.conf

$ cat /etc/httpd/conf/httpd.conf

DocumentRoot "/var/www/html"
...
<Directory />
    AllowOverride none
    Require all denied
</Directory>
...
<Directory "/var/www">
    AllowOverride None
    Require all granted
</Directory>
<Directory "/var/www/html">
    Options Indexes FollowSymLinks Includes
</Directory>

.htaccess

$ cat /var/www/html/.htaccess
RewriteEngine on
RewriteRule ^wiki/?(.*)$ /w/index.php?title=$1 [L,QSA]
<IfModule mod_deflate.c>
<FilesMatch "\.(js|css|html)$">
SetOutputFilter DEFLATE
</FilesMatch>
</IfModule>

footer.html is in the document root, sitting side-by-side with index.html. Its included like so in the relevant pages. Here is an example from Firefox's View Source option:

68 </UL>
69 <!--#include virtual="/footer.html" --> 
70 </BODY>
71 </HTML>

footer.html is available here. I got the <!--#include virtual="/footer.html" --> from Apache's manual on Server Side Includes (SSI) under Additional examples.

What is wrong with my configuration? Or, what am I doing wrong?