Almost 170 years ago, the internal combustion engine was born. It's a heat and pressure system, like a steam engine. Tell me after nearly 200 years we're still using these with no end in sight. Nothing has changed. It still uses mechanical pistons and crank shafts. They mostly create heat energy that is wasted by oxidizing fuel very quickly and expanding a gas to force the piston down. I'd say they are between 20-40% efficient energy conversion.
And electric? First you convert a fuel into mechanical motion, then convert that into electrical energy through a lossy transmission line, then store it into a chemical battery then convert that back into mechanical motion. So while electric motors may approach 90% efficiency the energy before reaching the motor has lost about 40% of its original potential.