Efficiencies might seem bad, but thermodynamics limits the efficiency of any heat engine (of which an ICE is one) according to the absolute temperature of the hot and cold side of an engine. This is called the "Carnot efficiency" and it's comparable to a no-friction mechanical system, or a no-resistance electrical circuit.

For an ICE, assuming combustion temperatures of 550K and assuming the radiator can cool the system to 50C, the Carnot efficiency is (1 - Tc/Th) = (1 - 333K/550K) = about 40%.

That's a hard theoretical limit that assumes all processes are reversible. Real engines have irreversible thermodynamic processes so the Carnot limit can never really be attained.

In other words, your complaint isn't with the engineers, it's with thermodynamics.

(note: ICE engines are modelled using the Otto cycle rather than the Carnot cycle, but that's a bit more complicated and leads to efficiencies that are even worse. The Carnot efficiency is an upper limit for all heat engines, including steam engines, Stirling engines, turbines, etc.)