I've seen conjecture that there is a real science behind this, but it doesn't involve the sticks per-se. In order to use them, there must be a focus on the thing you desire to find. This creates a sort of meditative trance with the sticks as the "focus" when in reality, the meditation is freeing up the conscious mind to not ignore the very subtle signs of an area being disturbed.

The fact is that they do indeed find bodies this way. The chances of randomly digging up a body by pure guess are vanishingly rare. We're talking at most around 10 square feet (often just 4-5 square feet) while there are 43,560 per acre or 27,878,400 per square mile. Even if you buried 1000 bodies in that square mile, your chances of finding one would still be a fraction of a percent.