Well, at the end of the day in this situation it is still humans that thought up the idea to separate the regions. I presume it is also humans who want to keep

Well, at the end of the day in this situation it is still humans that thought up the idea to separate the regions. I presume it is also humans who want to keep us-east-1 alive. Neither of those conditions (use1 going down or the cross DC contamination) are intentional. If us-east-1 goes dead because of a condition that humans failed to anticipate, then it stands to reason that the other regions are actually dependent on use1 in a way humans didn't anticipate.