There's one thing that I don't understand. You claim this coin is a circular economy. But what is stopping developers from withdrawing the coins

The developers can cash out / withdrawing.
They have an incentive to re-invest in advertising but that's up to them.
It's expectable that they cash out because that's how they make revenue. So the flow is: they first invest by doing advertising and then they cash out.
The cash out is done through an exchange.