I used to play this game in my pre-teen days, and what I love about this game is the weapons. They were memorable to me. I also liked the Veil as well. And I have to admit, I was scared of the Geists, but now I realize they're not that big of a problem.
Why should there be any? You're playing as a spy in a small german city within all german manufacturers and even resistance is german. Besides, what kind of gameplay diversifying element would bring thompson or colt to the game? Thompson almost identical to mp40 in everything other than lack of 2 bullets, yet it would function almost like clone. Not to mention it's stupid to have allied weapons in a german environment game, there would be no bullets for it. Nobody even used any allied weapons in original RTCW and the countless youtube videos is a solid evidence of that, so cutting them off completely is a good thing to do. Sure there are some in the black market shops, but these are mostly extremely rare trophy mostly for the show for marketing purpose.
Yeah, it makes sense since the whole story were involving in clandestine operations in german-occupied Europe so Allied weapons were not available (unless there are smuggled Thompson and Sten through underground movements or black markets)