It is a ring. Because of its structure. It is a webring. Just look at the bottom of this particular page to see how it works. Each site displays this fragment on its main page.
Visitors can now just hit 'Next' and they'll come to another member.
If they repeat it often enough they'll finally come back to where they started. So the word 'ring' is to be taken literally in this case. There are several arguments for this. Smaller sites are normally just ignored. In Abandonweb every single site is equal.