Prior to the war, relations between the US and Russia were relatively warm. Specifically, during the Bush War on Terror, Russia and China were active partners and enthusiastic participants in crushing “Radical Islamist Extremism”.
I suspect you can trace the reliance on Russian rockets back to that period, what with the end of the Shuttle program and a confused path forward between administrations.
Russian industrial rocketry was both world class and dirt cheap, back during the late '00s.