Available ads depend on how many advertisors are willing to spend money to advertise in your specific area. Ads are not shared evenly across the globe, because if they were you guys would be getting the swedish ads I get about water summer land trips to a random place in Skara and you would struggle trying to understand what a vattenrutschbana and familjeresa is.
If only a few advertisors in are interested in your area, you will only get a few ads.
If their interest is low, they will only invest a small amount of money as well so their ads will show fewer times overall.
If your specific area isn't appealing to any advertisor, you won't get any ads. Some users are in this situation.
On top of all this, ads are dropping in value and the CPM on this site is a horrifying indicator of what might happen to one of this site's best features if advertisors decide to demand advertisement for a cheaper buck.
This is why me and many other members sincerely hope that @staff will work to develop ways of coin earning that are not tied to ads in any way. One thing that me and another user (GoldenPlume) have suggested a lot is for tapas to team up with a reliable company that offers surveys for money, in order to offer users surveys for coins.
I know many silent creators and fans are wanting this too, they just aren't heard because they don't touch the forums and don't know/dare to use that one email adress tapas has listed somewhere for feedback and suggestions. They kinda just quietly wait in hopes that surveys or something else will arrive.