Why does the observable universe have an edge?
Unless amd until there is consensus among astrophysicista, there could be no affirmation that the observable universe has an edge
A planet's gravitational field has an edge for its near-zero gravitation. Similar edges could be imagined for a star's own system and a galaxy's own system.
Extension of the notion of Edge to our universe has to wait for consensus on the dimensionality of our universe and related further theories on the existence of multi universe..