There's a bug in TurnitinReviewServiceImpl's isSiteAcceptable logic such that it always returns false ootb.
Notice in ./pack/src/webapp/WEB-INF/components.xml, the ContentReviewServiceTii bean's siteAdvisor property is commented out; so siteAdvisor is null (ootb).
When the siteAdvisor is null, isSiteAcceptable behaves like a combination of all the site advisors - first returning if the site has a 'turnitin' site property. If it's not set, then it returns if the enabledSiteTypes contains the site type. If enabledSiteTypes is not set, then it's supposed to always return true.
However, the check whether enabledSiteTypes is set is going by whether it's null, but it is never null because init() sets it to Arrays.asList(ArrayUtils.nullToEmpty(...));
It should consider enabledSiteTypes to be set if only it's both not null and non-empty.