Eastern Europe specifically I'm too certain of, but in the case of the Soviet Union, they were in a position where they were able to observe a fellow Communist country embrace gradual opening of the market and of the industry - successfully - where their own programs had mostly failed to gain traction.

Mikhail Gorbachev, in particular, became general secretary in 1985 and by then was aware of how the Chinese managed to succeed where the Soviet Union had failed. Gorbachev's reaction, then, was to try to closely mimic the Chinese successes. He proposed to lease state land to the peasants, establish limited free trade zones, promote small businesses and joint ventures, and so on.

The key difference was that Gorbachev tried to impose these changes on an urban economy in which virtually all the citizens worked for the state, from the "top down". China, on the other hand, had worked from the "bottom up". Gorbachev’s reforms ended up either completely ignored or twisted into schemes that begun the process of enriching a very small minority (the present-day oligarchs of Russia). However, China's reforms, largely by the hand of Deng Xiaoping, simply chose not to oppose bottom-up reform that emanated largely from the rural population, and reacted accordingly when reforms became successful or faltered in specific areas, promoting what worked and denouncing what didn't.

TL;DR: The Soviet Union was in a position to observe Communist China gradually accept successful economic reforms, and reacted by attempting to do the same in their country under the leadership of Gorbachev; they tried to do so, however, by handing down orders from the top down, rather than letting the masses organize these changes from the bottom up. This difference in execution was the key to the failure of the Soviet Union to replicate Chinese successes.

Source: "How China Won and Russia Lost (2009)", by Paul Gregory and Kate Zhou