Supernova are localised phenomena. They take place in individual stars and the radiation they emit emanates from a specific time and location, an exploding star in a pre-existing universe. The 'big bang' is a different animal altogether. The 'big bang' is the origin of both time and space, not an event that took place at some point within it.
Technically, the 'big bang' was rendered invisible from the start. Due to the initial density of the universe, light was continually emitted and reabsorbed by surrounding matter. Only after the universe had expanded and cooled over many thousands of years did the universe become transparent to the light which is distributed more or less evenly throughout the universe and which now comprises the cosmic microwave background radiation.
As explained above, we can not directly observe the 'Big bang'. We are only witness to its remnants that permeate the universe it gave birth to and which point to its beginning. The portion of that remnant we observe at any given moment as the cosmic microwave background radiation, is the tiny fraction that at any given moment originated from the distance corresponding to the time we see it.