Paper dollars are a common store of value in emerging markets. Trading digital dollars for paper dollars, is becoming as common as paper foreign exchange

In practice, everyone just has binance app and pays each other stablecoins within that platform

The final settlement inside Somalia or North Korea isn't necessary because they can buy things from other countries where those people can do the settlement. Just like if you have US dollar bills in Somalia, they have value even if there is no nearby ATM you can find to deposit them.

There are already hawala / xawala money transfer services in Somalia that will exchange cryptocurrencies for physical dollars or local currency, or load value onto a local phone app. Does that answer your question? https://en.wikipedia.org/wiki/Hawala

So why are stablecoins needed if there is already a system?