I would also be interested in an answer to the mechanics of such sales/bundles.
I do can answer your immediate question. The discount is not visible on page, because the first item has no minimum price. But it is on discount, you can find it via tags and see a 50% discount banner. https://itch.io/game-assets/on-sale/tag-science-fiction/tag-side-scroller/tag-to...
But what does it mean to have 50% discount on a page without minimum price? There is individually priced file for $ 1.50. Will you get access to the file, if you pay $0.75 on a 50% discount? Will you get access to the file, if you buy it in a bundle and the bundle price was higher than $ 1.50 or does it split the bundle price among projects for calculation? I have no clue, and the faq does not cover the combination of discounts/bundles and indiviudally priced files.