The cost of developing 3 aircrafts is less than linear with the cost of developing one (there are some commonalities). The cost of developing one aircraft that meets the requirements of all, that can be astronomical, assuming a solution to that problem exists. Let's say you want a motorcycle-truck-helicopter that rides on rough terrain like a cross bike, carries 40 tons of goods like a truck and flies. Good luck with that :D
Designing a plane that can be used by the Air Force and Navy can be done; adding the vertical flight to it, you break it: it makes it fat (aerodynamic), heavy and all this for a use case that is rare and useless to the other branches. For example, an F18 can be used by USAF and Navy, a modified F16 can be adapted to carrier operation with a reasonable cost and still you have good planes. Take one of these and put the VTOL in it: there is no high-performance VTOL plane ever built, so what are we dreaming about?
Designing a plane that can be used by the Air Force and Navy can be done; adding the vertical flight to it, you break it: it makes it fat (aerodynamic), heavy and all this for a use case that is rare and useless to the other branches. For example, an F18 can be used by USAF and Navy, a modified F16 can be adapted to carrier operation with a reasonable cost and still you have good planes. Take one of these and put the VTOL in it: there is no high-performance VTOL plane ever built, so what are we dreaming about?