I don't understand why they advertise it. Even if tether burn all their usdt and just keep the supply at 100 usdt their coin's value still would be ~100 usd. So whats the point here for burning stable coins. If usd somehow got burn maybe we could get some benefits. Please explain me whats happening here what is the benefits for this burning.

On chain trackers did the announcement, I've never seen Circle announcing their token burning at all from their official channels. It's usually some twitter account that tracks events happening inside the Ethereum to give out some information.
I agree, even if only 100 USDT left in circulation, it won't change a thing because it's stablecoin and the fact that the image painting as if those burned stablecoin should've been 35k BTC spot bid is very misleading.