They got all that turf to the east they could use.
The hell that land got thats special and different from the other trillions of miles of land that Russia already got? Let the people decide and if the Ukranians wanna dip then they can, and same for the Russians. No need to kill the civilians.
"Ukraine has extremely rich and complementary mineral resources in high concentrations and close proximity to each other. The country has abundant reserves of coal, iron ore, natural gas, manganese, salt, oil, graphite, sulfur, kaolin, titanium, nickel, magnesium, timber, and mercury."
They won't fight over a piece of land this much unless they can extract something of value from it.