Yes. The idea was to keep the engines (and engineers) out of the hands of the other likely buyers. You've seen how soviet military surplus gets around: the same channels work for rocket engines, and those engines work in ICBMs just as well as they work in orbital launch platforms.
I don't know how effective this was. Did it backfire by promoting economies of scale in a program that went on to sell to adversaries anyway? Did it murder the domestic engine programs and did that have knock-on consequences? I don't know if the policy was effective, but I do know that stopping "engine proliferation" was a widely given and accepted reason for those programs.
I don't know how effective this was. Did it backfire by promoting economies of scale in a program that went on to sell to adversaries anyway? Did it murder the domestic engine programs and did that have knock-on consequences? I don't know if the policy was effective, but I do know that stopping "engine proliferation" was a widely given and accepted reason for those programs.