Sulphur and rest of the elements of group 16 are less electro negative than oxygen. Therefore, their atoms cannot take up electrons easily. They can acquire ${\mathrm{ns}}^2{\mathrm{np}}^6$ configuration by sharing two electrons with the atoms of other elements and thus, exhibit +2 oxidation state in their compounds.  In addition to this, their atoms have vacant d-orbitals in their valence shell to which electrons can be promoted from the p and s-orbitals of the same shell.  As a result, they can show +4 and +6 oxidation states