John Garand built the prototypes for what would become the M1 battle rifle in .276 Pedersen. He chose that round because in the 1920's the Army's ordnance bureau had conducted a study concluding the the "Goldilocks" caliber was .27-.28 -- the best compromise of lethality, recoil and ammunition weight -- and the Pedersen was a decent round that fit that bill.
When Garand's design won the competition (over, ironically, John Pedersen's own rifle), Secretary of the Army Douglas MacArthur made acceptance of Garand's rifle contingent on it being converted to use the .30-06 Springfield round on account of he had more than 3 billion rounds of the stuff left over from The Great War sitting in munitions depots.
So the .30-cal wasn't the first choice but it was forced on them by economics.
Garand also prototyped it with "primer actuation," which probably would have been a disaster in a military rifle, so not everything he did was brilliant.
Garand's first prototype also had a detachable box magazine because Garand had seen what a combat multiplier Browning's M1918 BAR was, and it had 20-rd detachable box magazines. But Army OB put the kibosh on that, too, insisting that all submissions use a fixed internal magazine of no more than ten rounds capacity. Garand sometimes gets "blamed" for that oversight but it wasn't his choice.
And RE: the .30-06, the first production models of the M1903 Springfield rifle had iron sights calibrated and marked to 2800 yards (image below), almost 1.6 miles. On later versions it was reduced to 2400 yards. And in the hands of a competent marksman, they could in fact hit an "area target" at those ranges. But it was always a waste of resources to give every grunt a rifle with that sort of potential.
