Good question.Why not? I mean Ukraine as Russia says is artificial country and needs to be wiped out. Shouldn't Finland be treated the same since it was also part of Russia and Russia can decided to take it back?
There is a big difference between Ukraine and Finland.
Ukraine is the birthplace of Russia a Slavic nation. Go read their history. It all started in Kyiv. Russia is a big brother of Ukraine.
Ukraine was intact built by the Bolsheviks.
Secondly it wasn't until Ukraine wanted to join NATO ,Russia decided to invade Ukraine. Without NATO and cozying up with the west to undermine Russia in the region ,Ukraine can exist or else it will become part of Russia.