Short answer: it's filtering out the outlets that don't accept your type of submission.
Using a standard credit? It's only showing the blogs that accept that type. Using premium? Then it filters the outlets that accept premium credits. Sharing a hip-hop track? It'll show you outlets that accept hip-hop. Uploading via SoundCloud? You get the point.
Want to browse the full list?
If you're researching curators rather than submitting a specific song, head to submithub.com/curators. That page shows every curator on SubmitHub, with filters for genre, country, type, and more. No track-specific filtering, since there's no track attached. Great for getting a sense of who's out there before you upload anything, or for digging into a niche (like Christian curators) without missing anyone.
The same goes for submithub.com/influencers on the influencer side.