Whatever the cause is, it isn't social behavior. They don't have mechanisms in their behavior for social behavior.

That doesn't mean that they are ignoring each other. It could be competition, it could be sharing warmth, it could even be a sense of security seeing another python.. "Hey, that python is hiding somewhere, I bet that means it is safe".

They MIGHT be ignoring each other as best as they can.

My personal guess is that they are seeking as much heat as they can. A 120G glass aquarium is freaking hard to heat. Another note: one ball python remaining on top of the other is a common sign of a python asserting dominance.