Brave Browser is an awesome tool focused in bringing the most safe and pleasurable browsing on the decentralized internet, and many users seems to don't understand effectively how the software works, the same on that will make you earn some BAT.
Let's assume you are in a region that Ads in Brave Rewards are supported, that doesn't mean you will receive as many ads you want...the ads are based in your browsing history and must be also available in the brave ads catalogue.
Other factor that can also be determined to ads displaying is your region, many users can say "why I am not getting them in daily or hourly basis", well as I can say is that the ads are not about quantity, but about the right ones each user deserves based in their own browsing history.
The software is respecting your privacy also here, showing the ads in the matters that you, as a user, normally research about, if you for example, receive a topic ad that you never researched about, how can you say the browser is respecting your privacy!!
Other thing also that can happen, you may see a lot of ads today but tommorow, you may not see none!
The feature is perfectly understandable as, regions has ads dedicated to that region, and if all has been shown, of course they won't be seen tomorrow!