Ukraine has lots of valuable natural resources, but Russia has much more of everything. The biggest reason for the invasion is most likely that Putin could not let a “brother nation” prosper and drift towards Europe and being a functioning democracy.

Russia’s population might get wild ideas if they saw that their Ukrainian cousins’ standard of living starts to rise rapidly while they have to endure living under a fascist dictator. And substandard and underdeveloped infrastructure, due to the rampant corruption and a government who doesn’t give a shit about the areas outside the larger cities.