Why Do Pointers Point?
Pointers point for the same reason that retrieving dog breeds retrieve, it's something they were selectively bred for. Now, this doesn't mean that pointing is a totally new behavior that was artificially inculcated in these dogs. Rather, it's a natural behavior that was somewhat morphed, as it happened in several other breeds such as herding dogs like border collies, Australian cattle dogs and Australian shepherds.
To better understand why pointers point, it helps to gain a closer insight into predatory behaviors observed in certain animals. In many predators, you may notice how, upon sensing the presence of prey, the animal freezes for just a few split seconds prior to pouncing. This freeze is what hunters found productive when using dogs as hunting partners.
The truth is, if dogs retained their natural instincts, they would not have taken an utilitarian role which paved the path for the symbiotic relationship they developed with humans in the process of domestication. If a dog would therefore freeze and then jump in an attempt to kill birds, chances were high that the birds would have prematurely flown away, depriving the hunter of any chance of capture.
Instead, over the span of many years, specific dogs were selectively bred for their ability to control their impulses and freeze for longer times, just long enough for the hunter to sneak and cast a net over the birds. While initially pointing may have been more of a trained behavior, with time, as the best pointing specimens were bred with the best, pointing most likely starting becoming a natural behavior, with the dog performing it with little prompting needed.