Seems like the 7mm has been dished in favor of thirty caliber ever since Teddy Roosevelt and the rough riders got thier butt's shot to pieces by the spanish 7x57 mausers.
It has nothing to do with that.
We've always liked .30 cal here ever since smokeless powder came on the scene. Our first smokeless powder military rifle was the Krag in .30-40 (1892), then the M1903, 03A3 and M1 in .30-06, then the M-14 in .308
It became popular in the sporting world first on account of the ubiquitous .30-30 and Winchester rifle, and then by the flood of surplus military rifles and ammo in .30-06.
That said, we're not alone. Many nations adopted the .30 cal before we did, and many after:
.303 British (.311", Britain, 1888)
7.35 Cacarno (.295", Italy, 1938)
7.5x54 (.308", France, 1924/29)
7.5x55 (.308", Switzerland, 1889)
7.62x54R (.311", Russia, 1891)
7.62x45 (.309, Czechoslovakia, 1952)
7.62x39 (.311", Russia, 1943)
7.65x53 (.313", Argentina, 1889)
7.7x58 (.311", Japan, 1939)
Then there were handgun cartridges, the 7.65 Luger, 7.65 Mauser, 7.62 Tokarev, 7.62 Nagant.
6.5mm takes second place around the world for military adoption
Except for the Germans/Austrians, 8mm was only used in machine guns (8x59 Breda, 8x53 Murata, 8x60 Swede)
The 7x57 (.275 Rigby in Britain) was the only 7mm cartridge adopted by a military; .280 British, .276 Enfield and .276 Pedersen failed.
There are a few European sporting 7mm's, but really only the 7x57 and 7x64 have ever enjoyed any real popularity there.
And we like the 7mm Rem Mag, but all the other .284 inchers have only been moderately successful. .280 Rem, .284 Winchester, 7mm WSM, 7mm STW, 7mm RUM all have only a small following, .280 being 2nd place to the 7mm RM by a huge margin.