Sales that recently ended or are older than 90 days are hidden. What region you are in effects what you see as well.
Like many websites now, I'm pretty sure ebay uses an algorithm based system as well. If you are a power seller, your items get seen by more people. If you pay extra to "promote" your listings, they get seen by more people. For searches, ebay choices what it thinks you want to see and doesn't always show you every result. You have to scroll past the recommended searches and dig a little deeper. At least that's from my experience.