Another interesting point, was that Brezhnev and his generation were the ones who fought WWII. Since 1914, with the Russian civil war and then WWII, Russia took extraordinary measures to deal with a threat to its territory; after the war it created a buffer of satellite states to protect itself from further threats.
Gorbachev and the new generation did not remember the war or external threats. They grew up with a relatively privileged position watching excessive repression for no valid reason they could understand, and thinking “there must be a better way”. Once they took over, they tried to implement a “better way”, only to find it did not include the old system at all.
The problems with the system were pretty simple - there was no real incentive to produce properly, and with central management rather than market forces, nothing worked. There’s the joke about the glass factory’s quota being in square meters of glass - so logically, they made up for low volume by producing glass too thin - so a lot broke before reaching the end users, wasting even more than if they had simply produced less but usable glass. Having met their quota or not, (or if they fudge the numbers) they still got paid.
As a result, the people had a lot of money, but nothing at the controlled prices to spend it on. Allowing any free/black markets simply displayed the worthlessness of that money and the scarcity of goods; and allowed some to get very rich, or others would take goods intended for regular retail and sell them extremely marked up on the black market.
There’s the story that when it rained, every car in Moscow pulled over to the side of the road and put the windshield wipers on. They were kept in the glovebox because otherwise, they would be stolen because you could not buy them at the store.