Because winning an offensive war is much much harder than winning a defensive war. Nobody defends anything better than they defend their homeland. Same reason russia can’t win the war in Ukraine. That’s why the first gulf war in early 90s was won too. US was fighting to defend Kuwait from Iraqi invasion. Once the US forced Iraqi army back to their side of the border, they negotiate a ceasfire. They only fought the war defensively alongside Kuwaiti fighters in Kuwait.
Because winning an offensive war is much much harder than winning a defensive war. Nobody defends anything better than they defend their homeland. Same reason russia can’t win the war in Ukraine. That’s why the first gulf war in early 90s was won too. US was fighting to defend Kuwait from Iraqi invasion. Once the US forced Iraqi army back to their side of the border, they negotiate a ceasfire. They only fought the war defensively alongside Kuwaiti fighters in Kuwait.