There is no reusable rocket available with 8.8 million pounds of thrust. And there certainly wasn't anything available when SLS was started. Falcon Heavy is about half the thrust of SLS. I agree that reusable would be much better, but reusability is a relatively recent innovation by SpaceX. SLS will get there. SpaceX is forcing everyone to up their game. In the meantime, no need to condemn them for not getting there yet during these transition years.
