Oh, I felt this one deep. Had a very similar experience trying to build a small SaaS marketplace a while back. The "great idea, empty room" problem is brutal when you've got a thousand affiliates all chasing the same product.
What actually moved the needle wasn't more listings. It was stacking the deck so early marketers felt like they couldn't lose.
Three things worked:
First, only let in software where I'd seen money already change hands - payment processor screenshots, existing MRR, or a proven funnel from a digital marketplace like Gumroad or Shopify. No pre-revenue "idea stage" nonsense.
Second, hard-filtered by audience match. Very clear ICP, traffic source, average order value, and proof they'd sold to that audience before. Marketers could instantly see "this is built for my list/channel" without guessing if it'd work.
Third, gave early marketers unfair terms - higher rev share, longer cookie windows, co-created funnels, and direct access to founders for fast iteration. That made them feel like partners, not just another link in a chain.
Used affiliate platforms to sanity-check who was already selling, then did manual research on social to see where those products already had organic pull. Took time, but stopped the "empty room" problem cold.