Just game design stuff, not extrinsic reward stuff. The game has a long build-up to conclusion. The idea is that you become more personally invested in the outcome of the game the longer you survive, giving you a higher emotional high the longer you can stay in the game. Emotional highs are how you become engaged with media. It doesn’t necessarily mean enjoyment either, you can just as easily become attached to experiences that provide frustration or anger - it depends on your personality.
In roguelikes, for example, the longer you survive the more likely you will find powerful equipment that will make completing the game possible. However, the longer you play, the more invested you are in your character (you’ve spent a lot of time on the character, you’ve found good equipment that’s let you survive so long). It’s really frustrating to die on floor 49 of a 50 floor roguelike. That frustration is part of what drives certain people to play again, drives others away, and drives some players to become toxic.
Contrast with modes like FPS deathmatch, where you receive continuous feedback. You can generally predict the outcome of the match early on, and it doesn’t really matter whether you make a mistake. You are not as invested. It’s certainly exciting to play and win deathmatch, but it’s not as frustrating when you lose. You don’t feel like you wasted any time.