Why does the Chicken cross the Road? Because she must.
The Chicken represents Life.
The Road represents Time and Age.
The edges of the Road are really two boundaries of the same plane, as it wrap around the world, forming the Great Unknown.
The Chicken MUST cross the Road, advancing in Age, as she goes.
Roads have a crown, so the first half of her journey is uphill.
When she reaches the dividing line in the center, she has reached middle age; it’s all downhill from there.
She comes from The Great Unknown, crosses, and so returns to The Great Unknown.
Thus, the answer is, because it is an existential imperative.
Or, it could just be absurdity built on misdirection, like, “what’s got four legs, is green, and would kill you if it fell out of a tree on top of you?” “I give up.” “A pool table.”