Hi Steven,
Good Day,
Let me explain you the current behaviour of the application,
Requester who belong to sites which are present under refer default settings (default configuration we provide) will have site has "Not associated to any site" when they create a request.
This is because all the sites which comes under the default settings will have the same configuration. (support groups,operational hours etc)
Requesters who belong to a site which has custom settings or copy default settings (changes made in the site configuration) will have the site name autopopulated when they create a request.