It seems to me that with a broader general historical awareness, you
would not ask these questions, or would ask different ones instead.
As to "who" makes decisions and how and why - go read the records from
past arms selections trials. They are readily available.
For example as a "different" question, you might ask when and where
availability of a new small arm was delayed by Congress not
appropriating the money necessary to purchase more than token
quantities of new arms and the ammunition they required and/or failing
to anticipate looming necessity for a lot more "new" weapons than were
on hand. Certainly that was the case with the Krag being empirically
slow in supplanting the trapdoor Springfield and in Springfield (03/
A3) production being fired up again for WWII when there were not
enough M1 Garands to be had.
In a context where there was no clear need to replace the trapdoor,
(the Indian Wars were won, America had no know foreign enemies, and
American was politically isolationist) there was little technological
point in replacing the trapdoor until the advantages of smokeless
powder were obvious. The Brits, after all, were still using Snyder
black powder single shots and world military doctrine saw a big,
heavy, slow, lead bullet as necessary to stop the HORSE in a cavalry
charge. The Brits had black powder Lee Metford repeaters, but
fouling was a problem in the rifles and the "small" 303 round driven
at black powder velocity and range would not definitively stop a
cavalry charge. You can probably peg the advantages of smokeless and
the weapons capabilities so enabled being OBVIOUS by about 1889.
There were French Lebels (using smokeless Poudre B) and the first
Mauser 1888's (using the German copy of Poudre B) a bit earlier, but
not in any quantity. And it took 6 years for the Brits to give up
(in 1894 when they adoped the then new Lee Enfield rifle) trying to
get the Lee-Metford repeaters to be reliable with cordite charged
loads.
My point is simply that the US Army had adopted the Krag (after
extensive tests) with smokeless loads in 1892 --- not exactly a big
delay after it was clear that this was a good idea. But Congress had
not funded equipping the entire regular Army with Krags (and not the
militias at all) when America was surprised by the Spanish American
War a few years later. There we found out that Mauser's were a bit
better than Krags. It really did not take very long at all to come up
with our own Mauser (the 1903 Springfield). As to decision makers in
government, TR made some pretty quick and clear decisions about the
Springfield 03. But, once again, Congress would not pay for enough of
the new Springfields for America's Army to be fully armed with them
(or even Krags!) come America's entrance to WWI. Fortunately,
America's arms makers (mostly Remington) had tooling on hand to build
the new British Rifle (the P-14 Enfield) which had been designed to be
quick and cheap to manufacture. Rechambered to 30-06, more American
soldiers went off to fight in France with 1917 Enfields than with 1903
Springfields. After WWI, the Army was indeed a bit provincial in
deciding the 03 Springfield was better than the "British" 1917.
Now, there is no doubt that America's M1 Garand equipped combat foot
soldier in WWII had more firepower than his British, French, Japanese,
German, or Russian equivalent. But, same story as before, the Garand
was adopted by the Army in 1936 and Congress did not fund fully
equipping even our small standing armed forces with them before Pearl
Harbor (at the end of 1941). So, when we needed rifles, out came
everything we had and we started making more 1903's using the tooling
which was still on hand too, But, except for the Marines that at the
outset were set in their ways with their beloved Springfield 03, we
pretty much made sure the combat battalions had M1's. So much for
your first paragraph.
I guess I would agree the M-14 is a great weapon, if for no other
reason than it is no more than an M1, shooting the slightly smaller
and slower 7.62 Nato cartridge (instead of the 30-06) with "select
fire" capability and a detachable magazine (rather than en-block
clip). At least for a couple of magazines (until it overheated), you
had the firepower of a mini BAR in your hands. Overheating, of
course, camouflaged its true chief liability --- like a BAR you pretty
much needed a couple of folks carrying ammo to sustain fire. But
"should have had it earlier in WWII" is pretty much nonsense because
what moron would have tried changing cartridges in the middle of a
war? This is exactly why the Brits fought WWII with the aging 303
round rather than adopting the 280 (with its slight, and largely
imaginary, advantage) as the British Army was want just before the
Nazi's invaded Poland.
Why didn't we pick the FAL? We did after all win the war. The M1
worked - and was a lot better than anything it opposed. M1 designs,
parts, and tooling mostly served for M-14 production. Why would any
sensible person change when the M-14 was an interim (and clearly
perceived as short-term) alternative and not obviously inferior to the
FAL in any clear way? Why didn't we pick the 280? Same story, not to
mention a total absence of any data (just like today) showing the 280
might be intrinsically superior. And the 7.62 Nato was indeed newer
technology which could use bullets and tooling already on hand!
In any event, the Nato round was not developed until 1954. So the
M-14 had nothing to do with WWII - at all. And your comments about
"better machine guns" back then are a bit mystifying too, since what
we use today is just a modestly improved John Browning (WWI) or before
design. And the M16 was deployed a few years after the M-14 simply
because the cartridges were small enough for a single soldier with a
select fire rifle to carry enough to, in theory, last through a fire
fight. In the dark, in the jungle, in Vietnam where you couldn't
visualize a target more than 20 feet away, firing lots of bullets was
a comfort. The only way to get a soldier to carry more cartridges is
make them smaller and lighter - which conventional wisdom says means
less powerful. So it really boils down to whether you want a more
power cartridge or more of them. And, the chief complaint about the
03 and the M1? They kicked too hard - something which pretty much
comes with the extra range and power. In these days where combat is
in more open country and in a time when light weight body armor is
readily available, the pendulum shifts in favor of more range and
power. Nothing about a 6.8 SPC is "special" or in and of itself a
significant technological advance,