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You are buying into the layman's view of engines, which is highly propagandized.

Engines should be designed to pursue volumetric efficiency (e.g. work per unit fuel), not gas mileage (which is nebulous and has nothing to do with engine efficiency).

In short, one of the 3 biggest losses (here, fuel burned that doesn't produce work) in an engine is heat soak into the cylinder walls, which you then have to burn extra fuel in pumps and fans to remove through a radiator. Because engine volume scales as the cube, while surface area scales as the square, it means necessarily larger engines are more efficient than smaller ones, and we see this is the case. Those big semi trucks actually use inline 6 engines with massive cylinders for efficiency, and the most efficient (regular, crankshaft) engine we know of is actually as large as a building. There are no other special qualities - it simply is large and thus efficient. https://en.wikipedia.org/wiki/W%C3%A4rtsil%C3%A4-Sulzer_RTA96-C

In short, moving to smaller engines has nothing to do with actual fuel efficiency, which scientists have been complaining about for a long time. Gas mileages are going up, while work done per unit fuel consumed is going down. It is devolution.

Also, the rotary engine is one of the four pinnacles of modern European civilization, along with the wristwatch (all of the complexity of the clock, but smaller), the jet engine, and the rocket. These devices are how we demonstrate our engineering prowess. Do you see what the jews are up to yet (Hint: 2 of the 4 have been phased out, and plans exist for the last 2)?