It seems mostly due to certain errors having attracted a large collector following. If it becomes well collected, it starts to make its way into the standard catalogues and trends.
There are many examples. Like the 1964 XWL 5c, all the "Arnpriors" silver dollars. A set I find notable would be the 1947 dot 5c, 25c and silver dollars. All of these are merely well placed die pits elevated to interesting due to the maple leaf issue.
And, there are some claims that the 1936 dot 25c, that was circulated, is just a die pit too. The bar is certainly just a die break in the right place.