Summary of Points1) What motivates bigfoot to avoid humans? 2) If bigfoot has special behavior to avoid humans and covers its own tracks, then this would require constant vigilance on their part, requiring significant energy and limiting their movements. 3) From an evolutionary perspective, its seems dubious that bigfoot would evolve such intricate behavior to avoid humans because their are no significant, fitness-reducing effects of encountering humans.Many bigfoot proponents believe that bigfoot actively avoids contact with humans. Even more remarkable, many believe that bigfoot will go to great lengths to avoid leaving tracks, even covering or obscuring tracks. If this is true, it would require extreme vigilance for bigfoot - they would have to be acutely aware of every movement they made, by making sure they weren't stepping in soft substrate that would leave a print, constantly scanning the horizon to make sure no human is around the corner, etc. This phenomenal behavior would require a fair amount of energy, and more importantly, it would result in significant opportunity costs, i.e., it would surely limit where bigfoot could go to forage, find mates, and how fast they could travel.
As would be true for all wildlife, such a unique and energy intensive behavior must be beneficial to the organism, and it must be subject to evolutionary principles, including natural selection. For a trait to evolve and persist, there must be a natural, selective force that reinforces the beneficial nature of the trait. For example, imagine a mouse that has evolved a special trait that causes the mouse the suddenly jump the moment a snake strikes. Mice that have this jumping trait survive more snake attacks, live longer, and reproduce more - in other words they are more fit. As long as snake attacks persist, evolution will favor the mice with the jumping trait. But if snakes suddenly become extinct, then the trait no longer provides a benefit to the mouse and natural selection no longer favors them over non-jumping mice. In fact, if the jumping trait requires the mouse to devote more energy to muscle development and sensory perception, then this energy is wasted and the mouse becomes less favorable in the eyes of natural selection. In that case, the theory of evolution tells us the jumping trait will gradually vanish from the population.
In the case of bigfoot, one has to wonder what evolutionary force is maintaining their special, secretive behavior over thousands of years. For bigfoot to evolve a trait that makes them spend significant effort avoiding humans, then there must be some detrimental cost of encountering a human. But what is that detrimental cost? We don't hunt or otherwise kill bigfoot. We don't harass or maim them. There are no historical accounts of Native Americans hunting or harassing bigfoot. And because we hardly ever even glimpse them, let alone come in close contact with them, I can't think of any routine, negative effect that would maintain such a complicated and energetically costly behavior. And while we can envision that potential encounters between humans and bigfoot could be costly to them, this doesn't mean that bigfoot can make the same conclusion since to date there are no negative costs to human-bigfoot encounters. Simply put, from an evolutionary perceptive, there is no basis for bigfoot to take such drastic actions to remain secretive.
I'm not arguing that bigfoot doesn't exist, I'm merely contradicting those that claim that bigfoot goes to great length to remain hidden from humans. The more likely explaination for the scarcity of bigfoot sightings is that they are extremely rare and prefer isolated, wilderness habitat.