Why start with a clean slate and develop a new plane? If the F-16 is still working, why not start with its design and upgrade the avionics and software?
One reason would be the age of the airframes. Technically, why not? But at a certain point you will need to compleely rebuild the airframes, like completely down to the last bolt and rivet. Only to still have an old airframe, in some sense. So new aircraft it is. And developing new enngines, avionics and software to put them into a new, and most likely modernized airframe, is frightingly close to a completly new aircraft design. And will give people the oppertunity to add features as well. And of course, because common sense doens't play a role in military development and procuremt for anything more complex than a Hummvee. Looking at the proposed Humvee replacements so...
