Why are the exhaust pipes design on the Ilyushin Il-2 not very popular? This is a piece of this image from Wikipedia



Note the circled region. Movies often show exhaust fumes coming from those pipes when the engine is started. So I assume these are actual exhaust pipes.
This design doesn't appear very often, especially in modern piston engine airplanes. Why is this the case?
This engine is about 10 times more powerful than a modern average piston engine. With such power you get some useful thrust from exhaust power directly. This design helps to recover it. With a small SEP, noise and keeping exhaust smoke away from the cabin probably is more important. And it's not true that it's not popular. It's popular with single engine turbines. Source: Wikimedia (click for link)