It’s not that the balance of power was convenient is that a major disturbance in it could’ve been deadly.
A civil war in the USSR at the time could have literarily ended the world as we know it.
The fact that the only major thing we got at the fall of the USSR was the attempted 1991 ‘August Coup’ is a miracle as things could’ve ended so badly for Russia and the entire world.
Except grain, which the USA provided in vast quantities to the USSR in order to prop-up its system in the wake of poor harvests.
There was a brief blip in 1980 when President Carter vetoed it, before resuming under President Reagan.
Why not use it as a lever to bring down the Soviet system 20 years earlier? Because the balance of power was quite convenient.