Why not CH-53K?
Horses for courses really. If you need a very heavy USL moved or a large amount of people for admin purposes then the -53K is an attractive, if unproven, option. Doubtless it will have better running costs and be more relaible than the hideously expensive legacy model (which make a CH47 look cheap...) and will have all sorts of swanky toys. However, if you wish to conduct assault operations in high DA / dusty environments then the -47 wins hands down thanks to the tandem rotor configuration. Why? No DA tail rotor authority issues, the ability to conduct rapid tactical decelerations onto the ground, a relative imperviousness to wind direction (except at high auw), a proven dust landing technique thanks to rear wheels and thats all before the -47F advanced avionics and flight control system are taken into consideration.
How many -53Ks ordered? 130ish for the USMC and it's sliding right all the time. How many -47Fs? 500+ and counting for the US Army, RAF, Dutch, Italians, UAE, Canada, Australia etc etc. Like I said, horses for courses....