Why are there no representatives of the Soviet Union in the "Imperial Capital Holy Grail Strange Story/Legend of the Imperial Capital Grail" in Fate/type Redline?

I can't accept an answer along the lines of "It's politically/ideologically inappropriate."

Let me clarify. Aside from the purely Japanese cast of parochial characters like "Demon Musashi"—who the hell is that?—and, on the other hand, the wonderful duo of the magnificent Ryouma and Oryou, Red Line does feature foreign characters.

The Germans of the Third Reich include Major Reiter, who for some reason summoned the "homeless" samurai Okada Izou instead of some "true German hero," and Maxwell's Demon (actually a theoretical concept, not a heroic spirit—WTF?) and his master. Let me remind you that the Nazis are the genocidal guys who started World War II.

The Chinese are Lanlan Fang from Shanghai and her lancer Li Shuwen (I'm not pushing anything on anyone, but I think Li is much more interesting as a hand-to-hand assassin, since, after all, Servants don't usually expect a punch in the face). They, however, are the main victims of the Japanese Empire's war crimes and genocidal policies during the War—the Nanjing Renya, Unit 731, the comfort women, and so on... Nevertheless, the Chinese couple is present in the narrative.

The Japanese Militarists are Reiji Magatsu and his firm, aiming to exalt the influence of the magical faction in the Empire through its use in battles and, consequently, prolonging the war as much as possible. In short, a faction of war criminals and fanatical nationalists, a kind of embodiment of Japan's dark past.

The film features cameo appearances by US Air Force pilots flying bombing missions to Japan, particularly the city of Tokyo, a city of millions. Bad guys?

So, all these guys and girls are in the story, despite their "inconvenience," but there's not a word about the USSR, even in the context of World War II. So, what's the big deal?