Snakeheads are a very popular food fish in Southeast Asia. And that is why they Asians illegally released them here. It is a fish they were familiar with and they liked to catch and eat. But they spread and don't have much in the way of natural predators. For what it is worth, all species of carp are also invasive species. Not one of them is native to North America. They are from Europe and Asia and were brought here because the people from those areas liked them and they got loose into the waterways. Brown trout are another European import. And then don't forget that we Americans have also done the same thing. Look at rainbow trout, they are native to the Pacific area but that is the most commonly stocked and caught trout in the land. Stocking rainbows has resulted in serious damages to native populations of cutthroat, golden and brook trout.
Stocking invasive or non-native species has been going on for a long, long time.