As far as I know the U.S. was the only nation in WW2 to use a semi-automatic as a main battle rifle. Germany, Great Britain
, Japan
, U.S.
S.R. and
all the other combatants all used bolts.
The Garand was already well along in development by December/41.
The other nations were already at war and it's very difficult to change your
main armament while maintaining a flow of weapons into service.
The U.S. transition from Springfield to Garand was quite smooth but their
war production was just ramping up at that point.
By 1945 U.S. production had reached astounding levels.
It really was the " Arsenal of Democracy".
There was also a prevailing opinion in senior military ranks of all nations that an infantryman could not be trusted with an automatic rifle
as he would expend all of his allotted ammo in no time. Wasn't true but that was the opinion.