The .30 cal was too big, and they tried to make a .276, but the Army thought that round not powerful enough, plus there was a lot of .30 lying around and the Depression was on and it would be expensive to switch over if the .30 could be made to work in the .276's action.
Later, the .30 cal was too big, and they tried to make a .276, but the army thought that round not powerful enough, so, what the hey let's make a shorter .30 instead, and see if that could be made to work, recoil-wise on full auto in a shoulder rifle.
Later, the .30 cal was too big (recoil), and they stepped it down to .22, totally stepping past the .276 this time. Nearly no one liked the new .22 poodle-shooter. And many still don't.
You'd think that one of these decades they'll go ahead and adopt that .276. If only MacArthur had given it all the green light in the 1930s. Imagine WWII with M1919's firing .276, and 10-shot Garands, and re-chambered BAR's