The empire was collapsing on itself. USSR occupied nearly 1/6 of the total landmass, it had on the ground every imaginable element in the periodic table and yet it was not a self sustained developed country. Large part of it was corruption and constant stealing on every level possible, but also the fact that all of its economy was managed by what comes effectively down to a large Excel sheet - completely top down.

Gorbachev tried to turn it around and failed. Fortunately he was a great man because he had a lot of humility and he allowed to fall it apart gracefully (relatively speaking). This gave freedom (from Russians) to many nations, yet too many of them are still imprisoned within Russian Federation (the name is a hint - it's not Russia but a federation of many nations) and I think of it as a great tragedy, especially now, when mainly the minority nations are sent to kill Ukrainians and to get killed instead of Russians.