Why not to cohabitate any snake

[Skiploder]

These snakes represented here were emaciated and spines showing, it probably didn't matter as to what they were eating, as long as it was alive and it was meat.
As for them in the wild, natural selection tells them what they need to eat, as the ones that survive will probably eat from the same source, and the ones that don't die, creating an ecosystem most likely that doesn't need thought or calibration on the prey size they want to eat.
More knowledgeable people please correct me if I'm wrong.

You are onto something. You're close....

Cannibalism in snakes that normally are not ophiophagus has often been observed to result in the fatality of both participants. This further reinforces that it's not natural behavior and may be triggered by something other than normal predatory instincts. I mean if the act results in the death of the diner and the main course - how could any one argue it is normal behavior? Evolution doesn't work that way.

When you take into account that ball pythons are known to communally share denning sites, we can safely deduce they are not obligate cannibals. Such behavior would work against adaptations that assist in their survival. So what causes a starving, stressed animal to kill and eat something it normally would not try to eat?

The fancy scientific explanation:

The term "energetically stressed" accounts for this phenomenon and it has actual been studied in snakes with regards to cannibalism in non-cannibalistic species.

Energy is the primary behavior motivator in animals. Energetically stressed animals are known to modify their behavior in various seemingly unnatural ways in order to meet this critical demand.

In order to prevent an energetic shortfall, animals often increase their search activity to find food. When they become so energetically stressed that they reach a critical tipping point, they will attempt to predate on prey items which incur a greater risk either of predation or defensive injuries.

In some studies, non-ophiophagus snakes would first cannibalize dead members of their own species when faced with a paucity of food. If already deceased members of their own species were unavailable, they would try to cannibalize living brethren. As they were not suited for taking down ophiophagus prey, the attempts more often than not ended up in death for all involved. The reason for this? Snake eating requires some highly specialized modifications. Even if the eater was able to subdue the victim, a fundamental inability to properly ingest another snake (have you ever seen how a Clelia or Drymarchon eats another snake?) would result in death to the diner.

If you stick a starving snake in a stressful situation (new surroundings, unfamiliar motion) with another animal, that stress results in a increased demand for energy in an energetically stressed animal. In a panic to combat this energetic deficit, the snake tries to kill and eat the nearest thing it "thinks" it can eat - even if that thing isn't normally part of the menu, or even if that thing is something they may not be able to ingest/digest.

Cohabitation did not kill these animals. Stress and starvation (energy stress) did.

In a proper set up, with properly fed animals, where stress was kept to normal levels, where environmental parameters were correct, and where adequate space was provided, this would not have happened.