Rune
Once A Fool
That didn’t stop them from using machine guns and Stark weaponry in Iron Man. But maybe that was a franchised branch?Also, there's a point about his origins - the guy is a thousand years old. So, his minions use things that are reminiscent of his original culture - updated crossbows and Asian weaponry. Machine guns are... very European.
Of course it could just be as simple as this: where the various films differ in genre, the rules of the MCU differ in minor ways to reflect it.
This would also explain the super-human traits of the Black Widows that I’ve seen complaints about; that kind of physics-defying action is exactly the kind of thing we’d see in any other super-spy action movie.