Because more advertisers are paying to show ads in that area. If you want more, then reach out to businesses around you and encourage them to advertise with Brave.
This has been going on for over a month now. Guessing you just now noticed. Please make sure you read everything at PSA: Unsupported Region and I do mean to read everything in that topic. It will provide you with a lot of info.
There’s no discrimination. Until today, nobody in the world was able to link to Uphold. This was down for over 2 weeks. Now it’s limited to only 19 countries. Unfortunately Turkey isn’t on that restricted list. This is a temporary change while Brave is working out some issues with compliance and fraud. Some countries will be brought back in a couple months while others will take longer. Nobody knows where Turkey will fall into things.