Welcome to aviation history.

If I am not mistaken, every large propeller driven plane manufactured since about 1958 (mostly Lockheed C-130s and P3s) is a turboprop. That was when the last DC-6B, DC-7 and Constellation were built. (There may be some non-American makes I don't know about.)

The larger an engine is, the more prone it is to failure from metal fatigue, which in turn is a vastly greater problem for piston engines than for turbines with their purely rotary motion. Thus, for large engines, the high initial cost of a turbine is offset by greater reliability and reduced frequency of maintenance. Small piston engines are less prone to that type of failure, and remain the engine of choice for the smallest light planes.

The old JT3 turbojet on the first 707s and DC-8s was a pure jet, meaning all of the thrust was directly from the exhaust out of the combustion chambers. It was very efficient in level flight in the stratosphere above speeds of about 550mph, but was excruciatingly feeble and noisy on the ground. The first jetliners used up about half their fuel just getting off the ground and climbing to cruising altitude, and could not make the north Atlantic crossings without stopping at Gander for fuel. The successor engine, the JT3D, had a fan added to the front end which generated thrust with cool air that bypassed the combustion chambers and rear turbine. It gave more thrust with lower fuel consumption and noise on takeoff and climb, more than offsetting the slight loss of efficency in level flight cruising. Modern engines have even more bypass, and are functionally more nearly like turboprops.

One might ask why the greater durability of large turbines has not led to more of them on railroads. The answer is that a railroad diesel is just as durable because of structural brute strength, at the cost of being way too heavy for use as an aircraft engine.