jewellery for men

As Salaam Mu Alaikum,
I understand that men are not supposed to wear jewellery, and limited amounts of silver is allowed.
If its possible could you inform me why it is that gold and titanium is not allowed for men, especially titanium.I do not intend on buying an item made from it, I would just like to know why?
Jazakallah,
Wa Alaykum Salaam.