Welcome to the iNat Forum!
Adding larger places analogous to biogeographic realms (though the terminology varies slightly) has been a common topic on the forum, so I’ve added your post to this previous thread and reopened it. This thread and links in the comments above will have a lot of info about why many large places aren’t on iNat and ways that users get around this (using combinations of places, projects, etc.).
A good response from staff about one of the main reasons why these places aren’t on iNat is:
https://forum.inaturalist.org/t/implement-standard-marine-places-for-the-worlds-oceans/1458/14
On a side note, when submitting a Feature Request (which the post above was initially submitted as), please be sure to fill out the required template. Requests generally won’t be approved if it is not completed.