Theism and Belief: Why is the Burden on Us?

An atheist and a theist engage in a friendly debate about the topic of god; specifically, whether or not one exists. The crux of the atheists' argument is essentially that the evidence for the existence of a god is lacking and has not led to the acceptance (on the part of said atheist) of the hypothesis that such a being exists. The theists' bottom line sentiment is that the evidence is sufficient for people all around the world (him or herself included) and it is up to the atheist to accept this evidence/open their heart/be open minded etc (there are many platitudes that are used in this situation).

This discussion has taken place innumerable amounts of times throughout history, and I don't see any reason to believe that it will not continue to do so for at least the foreseeable future. What I find particularly striking about this fact is that the existence of god is one of the few topics for which it is acceptable to claim that the burden of belief/being convinced lies not on the strength of the evidence put forth to bolster the claim but rather on the target(s) of said claims. A few other topics for which this is true are UFO's, bigfoot and the Illuminati/New World Order. Would anyone care to venture a guess as to what it is that these topics have in common? 

There is no proof that any of them exist (none of them do in my not so humble opinion).