During Perestroika, Gorbachev oversaw some market system type reforms that led to the rise of a class of proto-capitalist businessmen. When the USSR fell, these politically connected businessmen were able to buy up state assets of Russia and Ukraine for peanuts and became billionaires overnight. Their power was such that collectively they dwarfed the power of the state. They could buy off whatever politicians, judge, or official they wanted. And they had an army of paid assassins and thugs on their payroll to handle any dispute. Think of 1980's Columbia andthe cartels except far worse. Belarus was the only country that avoided this fate because Lukashenko essentially instituted a Stalinist-style dictatorship there. This brought its own set of problems but crime wasn't one of them and to this day Minsk is one of the cleanest and safest cities in Eastern Europe.
When Putin came to power in 2000, everyone assumed business would go on as usual. But what nobody knew was that Putin and his FSB pals had been quietly waiting for this opportunity for years and Putin oversaw what was for all intents and purposes an officer's coup. The FSB took back control of the government and went to war against the Oligarchs. Putin offered the Oligarchs a bargain: disavow all involvement the political system and keep you get to keep your fortune- refuse and face exile, arrest, or death. Many of Russia's worst Oligarchs fled to London. Some fought and were jailed. A few died under mysterious circumstances. And in the end all that remained were the Oligarchs who had agreed to take the deal. The Russian based Oligarchs were brought to heel. This ended the misery and chaos of the 1990's in Russia. The Oligarchs in Russia now answer to the state rather than the other way around.
In Ukraine that never happened. Oligarchs controlled all the media outlets, all the major industries, and owned most of the legislators and all of the Presidents from 1991 all the way until the current war. But like I said before, the war changed everything. So an Oligarch brokered peace is out of the question now. Putin had already broken the Russian Oligarchs and the war itself has broken the Ukrainian Oligarchs. The war has destroyed the Ukrainian economy and most of the assets that form the basis of the Ukrainian Oligarchs' wealth have either been destroyed or seized by Russia. The Ukrainian Armed Forces are now the most powerful independent political force in Ukraine. Only they now have the power to realistically challenge the government.