Due to the high risk of thruster failure on the Boeing Starliner, NASA cannot risk putting astronauts in it for the return trip to earth.
Boeing was paid $4.2 billion and has failed on two different test flights to achieve mission objectives.
SpaceX was paid $2.6 billion for Dragon Crew and reached space in 2020 and has delivered numerous missions with cargo and 49 astronauts to the Space Station.