Indexing is the right diagnosis and I won't repeat it. The one thing nobody in this thread has checked is your price, and that is usually the first thing a seller changes after zero sales.
I measured the game-assets top sellers on itch.io on 21 September 2026, three pages of the category's own sales ranking: 108 listings, 68 of them paid. Median paid price $9.99. 52.9% of the paid ones sit between $1 and $10. Cheapest $0.60, dearest $150.
Your core pack is $10.49 and your three expansions are $5.59. That puts the core within 5% of the median of what actually sells in your category, and the expansions below it. So whatever is blocking the sales, being too expensive is not it. If your next move after this thread was another price cut, that is the one change the numbers argue against.
You also already have a 30% sale running, so that lever is spent. Until the pages are indexed you have no traffic to price-test against, and a cut now would only lower the ceiling for the day the traffic arrives.