>>12391301You might want to rephrase your question to be a little more specific. "Why" can be interpreted in a number of ways, ranging from the proximal cause in terms of mechanosensation to the ultimate cause in terms of evolutionary pressures that caused taking a shit to feel good.
In case you were asking about the latter: just consider the alternative. An animal that is in agony every time it takes a dump isn't going to be inclined to take a dump whenever the urge arises, and so is likely to have a less efficient digestive habit. That in turn is likely to lower its fitness in the evolutionary sense of the word. Therefore, it's likely that pressures are such that taking a shit feels good.
