Because they are different products, even if the GitLab marketing pages make it appear as if they are the same.
(I'm not saying Gitlab doesn't have strings attached)
Edit: Confirmed, "GitHub Enterprise is delivered as a virtual appliance that includes all software required to get up and running. The only additional software required is a compatible virtual machine environment." https://enterprise.github.com/faq
If you want to use premium features, you do have to pay to unlock them, and depending on your deployment you would need to get the gitlab-ee image instead of the gitlab-ce one.
Things like code review tools would be hosted in Virginia [eqiad] (with backup in texas [codfw]) on hardware owned by the Wikimedia Foundation.
Docs about how gerrit is hosted https://wikitech.wikimedia.org/wiki/Gerrit if you want to know nitty gritty details see also https://github.com/wikimedia/puppet