It looks like Ukraine is trying to capture the Donbas. If they do that, or just come close there will be no escape for Russians in the south through the Donbas. The only land route left will be the Kerch Strait.
In war you don't want to give your enemy an escape route. The ideal offensive traps a large force with no supply and no escape. Then there are only two outcomes: the siege is relieved by outside forces breaking through the lines (which won't happen with this terrain), the surrounded units surrender, or they fight to the last like the Imperial Japanese. Russian morale is way too low to fight to the last, so surrender will become inevitable.
Then Putin needs to try and weather the most humiliating defeat possible: loss of the entire army.
Perun points out that all those babushkas crying when liberated by the Ukrainians are Russian speakers. The claim the Ukrainians were discriminating against Russian speakers was just propaganda.
The Russians were able to get some people in the Donbas to fight against Kyiv because the Donbas is the poorest region in Ukraine and there were some people who figured Russia couldn't be much worse. Now after 8 years of low scale war and 7 months of brutal war that has killed a huge chunk of the male population of Donbas there are probably quite a few of the survivors who are thinking peaceful poverty in Ukraine probably beats genocide under Russia.
Crimea was always more pro-Russian. In the vote to leave the USSR the leave vote was weakest in Crimea. It's also notable that we haven't heard stories of Crimean men being pressed ganged into cannon fodder units like the men of the Donbas. Crimea might be somewhat more tepid about returning to Ukraine, but there are probably plenty of pro-Ukrainians there too. The partisans have been active there and it's difficult to run a partisan operation without civilian help.