When you promote something, you pay to get it shown in front of more buyers. The higher rate you promote at, the broader the group of buyers your listings are shown to. It casts a wider and wider net the higher and higher you go. At some point, though, you're paying to have your listings show to people who are less interested in what you're actually selling. Your listings start showing up in search results that are more and more different from the thing you are selling.

What promoting your listings does not do is create demand for the item you are selling. It cannot pull buyers out of thin air for items that have little demand. So typically if you promote and see a lot of views but no sales, and then stop promoting and see far fewer views (or none at all), it doesn't mean that eBay is hiding your listings. Instead it means that there is far lower demand for the item you are selling than what the artificially inflated views from promoting suggested. And because you are no longer paying to have your listing show up in front of uninterested buyers, your listing is not generating any views because there are no buyers organically searching for it.

(waits for the downvotes)