For a high skill player consistency is the difference between a 1st line player and a 2nd line player. Think Kostitsyn. AK47 had all the skills and size, and when he was on he impacted the game. But he often didn't show up and so he was a 2nd liner. Be inconsistent enough and you are gone. Talent without work results in nothing.
I think Andrei had some ehmmm work ethic problem. Demidov is a better playmaker too and shows a more consistent motor. Personnality wise they're really fart apart. Kostityn had all the tools but wasn't really productive in his draft year. It was a big development project that failed. Demidov is producing at superstar level (even if it's in the MHL). Way less risk involved.