The idiom asleep at the wheel is used to describe someone who is not paying attention to their responsibilities. If the babysitter is asleep at the wheel, they might not notice that little Johnny has eaten the whole chocolate cake on the kitchen counter.
Saying that someone is asleep at the wheel implies that a person in a position of control, "at the wheel," is failing to notice a problem that could lead to failure or disaster. If someone were literally asleep at the wheel while driving, the consequences could be catastrophic. That's the idea behind the metaphorical idiom. Whether it's a manager ignoring a budget crisis or a government agency failing to respond to warning signs, being "asleep at the wheel" suggests negligence or a lack of focus at a critical moment.