Having been intimately involved with numerous government projects I can tell you exactly why they haven’t chosen a design. No leadership. Somebody has to take charge and make critical decisions. Somebody has to arbitrate between the competing potential customers. Everybody wants THEIR version to be the one chosen. The moment you make a decision a whole range of options disappear. A simple example would be the F111 swing wing fighter bomber. One group wanted a fighter, which mean small, agile, maneuverable and fast. Another group wanted a bomber. I think it was Secretary McNamara who decided one plane could do both. (Also, the father of the one gun for all applications, the M16.) A plane big enough to carry a significant bomb load was a poor fighter plane. A plane maneuverable enough and fast enough to be a fighter was a poor bomber. The plane did nothing well. I’ll bet the same arguments are happening now. Somebody wants a heavy lift vehicle and somebody just wants a space taxi.
Not quite (it was worse)
The airforce wanted an aircraft, nominally a "fighter". whose real purpose was to sit in a bunker in West Germany, until Der Tag. When it would head out, easterly, just above the tree tops, carrying what the military likes to call a "special store" in its belly. This said a big heavy aircraft with the structure strength and fuel load to punch through the thick turbulent air at ground level.
The navy's fighter actually had to carry a far heavier load of six Phoenix missiles up to altitude, then cruise around slowly, burning as little fuel as possible.
Result, a big heavy aircraft (too big to operate off carriers) with an engine originally planned for a mid-50s commercial jet. Not a happy marriage.