Here's why:
* Tribute Summoning Timing: Tribute Summoning is a main phase action. You can only perform it during your Main Phase 1 or Main Phase 2.
* Battle Step Restrictions: The Battle Step is dedicated to attacking and defending. You can only perform actions that are specifically allowed during the Battle Step, like attacking, changing your battle position, and activating certain card effects.
Therefore, you cannot tribute summon during your battle step, even if you have "Nest" in your hand.
Let me know if you have any other Yu-Gi-Oh! questions!