Why is the exhaust gas temperature so hot?

The exhaust gas temperature of combustion engines is between 600°C and 900°C. Is it not possible to lower this temperature in order to generate more energy in the form of work? In this video, thermodynamic processes are used to explain why this is not possible.

Physik,Thermodynamik,Energie,Entropie,Arbeit,Wärme,Kreisprozess,Otto-Zyklus,physics,thermodynamics,energy,entropy,work,heat,thermodynamic cycle,Otto-cycle,Verbrennungsmotor,combustion engine,