I think soundtracks are just part of the swag section, where folks can add entries, but it's not, by any means, meant to be complete. It was a way for people to add soundtracks to their collection if they were bundled with game (but not part of a bigger limited edition bundle). This also applies to things like pre-order swag (like artbooks, keychains, etc.).
They are allowing the records to be added with the understanding that the site is focused on the games and game variants. Other categories like t-shirts and soundtracks will never be "complete" or super extensive as it's pretty much impossible without that being the focus of the site.