He was promised to be reborn in an ideal life on Earth after he kills Vandalieu. Thus, he views this life as a throwaway. Also having his memories from his two former lives/deaths has damaged his psyche. The game-like systems (status screen, skills/abilities having levels, etc) of Lambda just cement his distorted view of reality.
The WN makes it clear that in Origin, they took their lives seriously because they were not told that they would be reincarnated into Lambda when they died. However, after multiple lives and being told they would get another if they killed Van, a not small percentage of the reincarnators would think of Lambda as just a place where the consequences of their actions don't matter (though Gungir is one of the worst).