Egh, well I think this is an important distinction to make. The game is successfully running on multiple cores, but it is not using multiple cores worth of total processing power. Your choice in terminology is misleading.
And this game using only ~20% of that person’s CPU is not necessarily a bad thing. What it likely points to is the game being GPU bound (as mentioned by Syed). Of course none of us here (as far as I know) are developers for Ark so we can’t do much in the way of profiling.