It is largely a statistical illusion - a huge part of Ukrainian economy is in the gray sector. However government transfers, budget spending and industry does show up in statistics.

The two Donbass oblasts actually scored high on GDP per capita, but had much lower quality of life indicators. A large reason for this disparity in income is government transfers, like the big pension and health benefits provided to mine workers. You also had huge indirect transfers like the government propping up failing enterprises and buying production from the regions industrial oligarchs.