system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why did the U.S Air Force retire the LGM-118 Peacekeeper Missile?
gpt
couple of reasons

when the Cold War ended, there wasn't a need for a massive number of land-based ICBMs. They have a fleet of various versions of the LGM-30s, and a new and expensive fleet of the LGM-118 coming into existence. It was easier and cheaper for them to simply do away with the LGM-118s for the continued use of the LGM-30s. 

By the time the LGM-118 came out, SLBMs (specifically the Trident II), were just as capable as the land based ballistic missiles, and almost infinitely more survivable.

So due to budget cuts, and nuclear reductions following the end of the Cold War and SMART, the LGM-118s were the logical choice. They didn't offer any major difference over the LGM-30s, they costed far more, and the Trident IIs were far more survivable.