There's different jets out there for different applications depending on the mission at hand.   See 3 other replies

Oh, okay that makes more sense to me now, thanks for the reply Rigs Man! See ya around!   See 3 other replies

The role that the plane would be placed in would require it to function in different ways. For example, the navy might not need the VTOL ability and so the main airframe might be configured differently. The fan lift might be removed to make room for electronic warfare equipment or extra fuel tanks. The marines, on the other hand, mightd want the fan lift b/c they don't need the range of extra fuel tanks but need the flexibility to take off from helicopter carriers, which don't have the deck length to accommodate a full-size fighter. Either way, if the gov't wants to give the contract to a company to make a one-size-fits-all airframe, then they can buy 100 planes and configure them as needed instead of buying 20 planes from one company, 30 from another and 50 from a third.   See 3 other replies