The way this actually works is that militarization occurs most heavily in geographically favorable parts of the border, so that the least surveilled parts are the most physically dangerous to cross. In this way, increased technological sophistication at the border increases the number of deaths in border crossings.
Border Patrol isn't out there rescuing thirsty migrants. In fact, they're known for destroying life-saving water caches and brutalizing activists who try to provide water or medical aid to people wandering that part of the desert.