Here's why:
* Stardust Dragon's effect: Stardust Dragon's effect is to negate the activation of a Spell/Trap card and destroy it. It does not negate the effects of monsters.
* Chaos Sorcerer's effect: Chaos Sorcerer's effect is a monster effect, not a Spell/Trap effect. It allows you to Special Summon a "Chaos" monster from your hand or Graveyard by tributing a monster.
Therefore, Stardust Dragon's effect cannot negate Chaos Sorcerer's effect because it only negates Spell/Trap cards, not monster effects.