SLS is a disposable product based on existing technology. Starship intends to be reusable and is an evolution based on tech developed in the last 20 years.
Neither private companies nor the DoD is interested in using the SLS once it has been proven in the Artemis project, and given the project is based on the time-honored tradition of government pork, it’s doubtful it will ever be economical. Every indication I can see is that the Blue Origin and SLS contract are to hedge bets in case Starship fails. After all, we know SLS will work, but it will always be cost-ineffective just based on the nature of the beast. Blue Origin might work out, but they’ve been around as long as SpaceX and have achieved suborbital flights so far. Meanwhile, SpaceX has had 332 successful launches in 14 years, with 2 failures. Their team seems to know what they’re doing.