The periodic table lists 118 known elements. Although all 118 elements, and possibly more, can be produced by natural processes, not all of them are commonly found in natural settings. Each of these elements has a unique atomic weight and properties that set it apart from other elements.
According to Wikipedia, many of the elements heavier than uranium are unstable, resulting in a relatively short half-life. The instability of these elements caused any naturally occurring deposits of them to decay into daughter elements long before human beings evolved to look for them, and so they may be regarded as not technically occurring in nature.