wondered if anyone knew what makes an engine manufacturer decide to go one way or another with these but can't find much on the net.
The engine guys will gladly build anything that an airplane manufacturer wants
but I'm sure that a better answers to come would be a list of pro & cons for the performance and maintenance aspects of the plane that the engine goes on.
Ideally some examples could be listed like the aft prop versions of the 80's and 90's that never sold.
Noise, vibration, CG balance, drag, and equivalent safety come to mind.