I think the people seeding these are also ideologs and so would be interested in also supporting the obscure stuff, maybe more than the popular. There is no way any casual listeners would go to the quite substantial trouble of using these archives.

Anyone who wants to listen to unlimited free music from a vast catalog with a nice interface can use YouTube/Google Music. If they don't like the ads they can get an ad blocker. Downloading to your own machine works well too.