It is simply the rate at which fuel can be burned. For instance, the Saturn V's first stage carried 1.37 million kg of liquid oxygen (along with the kerosene fuel), which it burned in about 165 seconds. Imagine the size of the jet intake you'd need for a comparable amount of air.
The turbojet engine develops most the thrust in the exhaust nozzle.
The turbofan engine develops most of the thrust in the fan.
No engine develops all thrust in the exhaust or in the fan. There is a balance between the two components
Exception makes the turbo shaft where the turbine absorbs all power from exhaust gas to drive the shaft. Both airplane and ...