All of you are only partially correct.
Yes, bad economics is the background. All Communist systems become increasingly inefficient, and despite whatever tinkering (so-called planning) is done, it will not improve.
But - what brought the Soviets down (and nearly brought the Chicoms down in May-June of 1989) are divisions and power struggles within the party itself. After the strong-man (ie. Mao/Stalin) destroys any rule of law, power naturally becomes dispersed among the bureaucrats who battle each-other over economic policy, power, control over the military, etc... In fact, they probably hate each other more than the outside enemy.
George Kennan knew this when he proposed “Containment” after WWII, and Reagan understood that, Totalitarian Gov’ts are, in fact, very weak internally.
Was a student of Kennan but not a fan. He was too content with maintaining relations enstead of changing them, same with Zbig To be fair perhaps he was just a product of his politacal environment. It took Reagan to challange the status quo.