I've been searching some things regarding the ability of sulfur to accomodate negative charge and reached the conclusion that it's due to its size and its ability to expand its valence shell.
I can't fully understand the expansion part though. It is mentioned in various sites and books that sulfur uses the 3d orbitals due to their similar energy level with 3p orbitals in order to achieve this "expansion". However, 4s are supposed to be filled first. I even came across this question: How does expansion of electron shells work? but the answer given didn't really helped me. So why do we consider the expansion to happen with 3d orbitals, while 4s is filled first?