The thing for me is that we (humanity that is) already know how to safely land a rocket booster and reuse it. SLS has been in development for quite a while, and lots of funding. So why aren't recovering the boosters part of the program? The most likely answer is that no one on the funding / direction side thought it was worth while, or possible, at a time when that could be engineered into the system. The cynic in me feels that there is more profit to be made in throwing away the boosters. I wonder if the true answer is somewhere in between?