Who says they are? One reason that you may think they are is because you aren't seeing light jets. The Honda jet has a wingspan of 12.1 m (39.8 ft). The Phenom 100, 12.3 m (40 ft 4 in). An older Learjet, 35 ft 7 in (10.84 m). But the King Air turboprop is 50 ft 3 in (15.32 m). read more
There are no passenger prop planes the size of 150+ seat jet airliners so this is one reason that the wings will be smaller. And turboprop planes fly at about two thirds the speed of a jet - say about half the speed of sound rather than mach.8 - given the limitations of propellers. read more
Turboprop - aircraft with propellers can actually be powered by a turbine combustion (jet) engine, which then directs the rotation to a gearbox driving a propeller. Many commuter aircraft are this way because of the reliability of turbine engines vs. reciprocating piston engines. read more
Propellers have a much higher effective disk area than pure jet engines do, and deliver way more thrust per installed engine power than pure jets do. The turbofan is much more fuel efficient than a pure jet because the large bypass fan works kind of like a propeller does. read more