Here's why:
* Initial Bloodbath: The opening moments of the Hunger Games are chaotic, with tributes scrambling for weapons and supplies. It's a dangerous time, and Katniss and Peeta prioritize staying hidden and safe.
* Cornucopia: They are initially near the Cornucopia, the central hub of the arena where supplies are gathered. The area is crowded with other tributes, making it unsafe to sleep.
* No Time for Sleep: The constant threat of attack and the adrenaline rush of the opening events keep them on high alert. They are too preoccupied with survival to even think about sleeping.
Instead of sleeping, they focus on gathering supplies and finding a more secluded location to rest later. They eventually find a cave where they feel somewhat safer to sleep.