I think you're drastically underestimating how stupid and over-confident people can be. He had a college education, but that doesn't teach you the survival skills needed to live in the wilderness. McCandless spent a few years bumming around the United states before traveling to Alaska which likely gave him a false sense of security in his survival abilities.

Most people living in western nations have no idea of how unforgiving the wilderness can be, nor do they understand the amount of effort that it can take to survive. The amount of tourists who think that national parks are just the outdoor equivalent of Disney Land is shocking.