Deep Mind is best understood as the following bet: if we can train an AI that can learn from "its environment" and do the sort of things a human would do in that situation, then we have achieved AGI and from that ... business ... will follow. Hence their focus on video games as a training environment.
This sounds intuitive but is actually a very agent-centric viewpoint and most AI doesn't resemble this type of thing at all. Most AI deployed so far doesn't have anything resembling an environment, doesn't have any kind of nexus of agency and doesn't need to actively make decisions that then feed back to its own learning, only make probabilistic predictions. And in fact you often don't want an ML model to train on the outcomes of its own decisions.