The Lunar Gateway exists so that SLS and Orion have a way to get to the Moon, because with it SLS can’t get into LLO and return to Earth, so they need another c

The Lunar Gateway exists so that SLS and Orion have a way to get to the Moon, because with it SLS can’t get into LLO and return to Earth, so they need another craft to finish the trip and a place to meet up with that craft. A reasonable question might be why not make Starship HLS act as its own gateway but then you start getting into why is SLS and Orion even needed.