Why does sulfur have more than 8 electrons in its valence?

The octet rules says that an atom can only have a maximum of 8 electrons in its valence shell. This applies from non-metals to metalloids to metals. In this case, sulfur can have more than 8 electrons in its valence when it acquires a larger state specifically in an ionic state. For example SO4 2 - where the 2 - adds to the number of valence electrons