Are you sure EE automatically force SSL to all sites by default? If you check /etc/nginx/conf.d directory you will see that
force-ssl-domain.conf config files are DOMAIN specific. It's not one force-ssl.conf file that automatically applies to all sites, it rather:
force-ssl-domain1.conf force-ssl-domain2.conf force-ssl-domain3.conf
etc.
Why would they do this then?