The Atlas V was designed at a time when the Soviet Union was crumbling. Using Russian engines was an American ploy to ensure world stability by keeping Russian rocket designers gainfully employed instead of leaving them fend for themselves, building God knows what for the highest bidder.
Did that work? Well, I haven't seen much progess in rocket technology by people crazy enough to start wars.
Has this tactic outlived its usefulness? Yes, in view of recent developments, it's time for a new arrangement. Oh, look, that's just what they're doing.