Why does standing still keep aggressive dogs from attacking you?

As a guy who likes to travel with friends by walking/hiking, we encounter unchained/unleashed packs of dogs every time. Some of us run away from fear of getting attacked while i and some of my friends understands that the dogs will not harm us when we stand still, but we don t know exactly why they don t attack us.
Update: Edit: I meant the dogs we encounter were already alerted by our presence and have already started barking at us. Probably to tell us to go away. But when we turn around and walk away/into a different path, they'll start coming for us. So some of us starts running away getting chased, until dogs'... show more Edit: I meant the dogs we encounter were already alerted by our presence and have already started barking at us. Probably to tell us to go away. But when we turn around and walk away/into a different path, they'll start coming for us. So some of us starts running away getting chased, until dogs' considerable distance then come for us who stood still. We always wait until they return back their homes or when the dog owner takes notice.
Update 2: Note that we live in the Philippines. The places we travel are mountain villages, and in those villages comes packs of territorial dogs. sometimes, inside the compounds/homes (behind gates), sometimes outside the homes.
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