Here's why:
* "Green Baboon" requires a specific condition: "Green Baboon" is a monster that can be Special Summoned from your hand by sending a "Crystal" monster from your hand to the Graveyard.
* Crystal monsters are NOT in the Spell & Trap card zone: Crystal monsters are monsters with the "Crystal" attribute, like "Crystal Seer" or "Crystal Beast Sapphire Pegasus." They reside in your hand, field, or graveyard.
* Spell & Trap cards are not monsters: The Spell & Trap card zone is where you place Spell and Trap cards, not monsters.
Therefore, destroying a crystal in the Spell & Trap card zone does not fulfill the condition to summon "Green Baboon".
To summon "Green Baboon", you need to send a "Crystal" monster from your hand to the graveyard.