The SLS was engineered with one overarching goal: to be politically un-cancelable (under normal political circumstances). And in that, so far it has wildly succeeded. There are so many parts and processes that touch on so many districts that are held by both parties that, until the recent “fuck it lets flip all the tables over” political era, killing it would be like touching a third rail. It was done this way as a specific reaction to the cancellation of the Constellation program.