They are more efficient because converting anything to heat is trivial. Heat is just losses basically. A process consisting of 100% losses is great for heat gen

They are more efficient because converting anything to heat is trivial. Heat is just losses basically. A process consisting of 100% losses is great for heat generation. However, extracting exergy (electricity is pure exergy) from a flow of energy is the tricky part and will always be associated with efficiencies way below unity, based on fundamental principles.