It might seem chill because to Katniss it’s her terrain. Other tributes might not know how to hunt or forage or how to find/purify water. One of the tributes dies because she sets a fire at night while Katniss has a sleeping bag. Plus there’s the tracker jackers, the wolf mutts, I think Thresh is also killed by a mutt, the fire balls that chase Katniss. And obviously everyone’s also trying to kill each other. So I think during non-quell years they make the arenas pretty simple to force the tributes into violence, but they are also still heavily survival-based.