The US 'ploughs its own furrow' with a new Infantry Rifle.

[ColinA]

It's simple if you look at it the right way.
The money is in developing and testing new ammunition and arms.
Nothing sexy about adding bells and whistles to 5.56 or 7.62!

If you are developing something "new" you can look for grants to research and develop it. You can have meetings with important people who all need taking to expensive meals. People can go on fact-finding visits. Just watch the money go around.

Knowing the American system, as soon as the Army accept a calibre the Navy will reject it and develop their own!