The United States is too culturally, demographically, and politically diverse to operate a unitary state. Just because certain laws work in Connecticut, that doesn't mean that they would work in Wyoming necessarily.
So then the unitary government would only craft laws that would work universally... meaning they'd either pass fewer laws or they'd be more complex, in these cases.
But I'm struggling to think of a good example of what you could mean?
For example gun laws, heavily urbanized states and areas should have different gun laws from more rural less densely populated states.