Why aren’t low budget airlines, for example Ryanair using turboprop in short haul flights from Dublin to Liverpool (Just an example, it’s about 200km) not using Turboprop but optin in using a Boeing 737?
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There are specific limits for each powerplant.
A turboprop can use a relatively very wide propeller. This allows to “push you forward” by taking a big mass of air, and pushing it back. Like paddling a raft with a pretty big row.
A turbofan has an enclosed “propeller” called fan and this limits the airmass you can work with. So, you paddle the raft with a smaller row. It’s less efficient. Your row will tend to “slip” through the water.
The advantage of a turbofan, is that you can shape the duct in front of the fan and after the fan. Fan and propellers need to work with air that is below the speed of sound. You can take almost speed of sound air, send it through a divergent duct, this slows the air down, you work that air with the fan, then a convergent duct accelerates the air to a speed close to speed of sound before ejecting it. This allows a turbofan to stay efficient while propelling a plane at very high speed, including speeds well beyond speed of sound. Again, the logic is: take air, transform speed into pressure, add energy, transform the worked air into very fast low pressure air, shoot it out.
When to chose one or the other: short flight won’t benefit much from very high speeds. You can use a slower plane, which means consuming less fuel due to airplane speed; for a slow target speed, having the “big row on the raft” is surely beneficial in terms of getting good thrust from each pound of fuel. So double profit, cheaper cruise speed and a powerplant very efficient for that task.
Then if the flight is longer, you prefer to sell a quicker mean of transport, a faster plane. A faster plane can only work efficiently with a turbofan, which is in the end a glorified propeller in a properly shaped duct.
Note: to understand the efficiency given by working a bigger air mass: do this experiment. You sit on an office chair, facing a wall, push with all your strenght the wall, by reaction, you will be propelled the other direction. Now do the same but instead of pushing the wall, push a colleague that is sitting on another office chair. Yes you propel yourself the other direction, but less, and part of your force is lost in shooting your colleague the opposite direction. The heavier your colleague, the more reaction you get. The lighter the colleague, the less you get. If you push an empty chair you won’t even move you will just shoot the empty chair away. That’s basically the difference in pushing a bigger or smaller mass with the goal of getting a reaction force.
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