Software development is not engineering because it is still relatively young and immature field. There is a joke where a mathematician, a physicist and a engineer are given a little red rubber ball and asked to find its volume. The mathematician measures the diameter and computes, the physicist immerses the ball into water and sees how much was displaced, and an the engineer looks it up in his "Little red rubber balls" reference.
Software development does not yet have anything that may even potentially grow into such a reference. If we decide to write it we would not even know where to start. We have mathematicians who write computer science papers; or physicists who test programs; standup comedians, philosophers, everyone. But not engineers.