> Why?

It generally requires rulemaking to be done pursuant to a public-comment period and not be done in a way that is "arbitrary and capricious." I'm not familiar with the Immigration & Nationalisation Act(s), (as amended), so I don't know the degree to which public comment is required and judicial review permitted, but a last-minute rule like this would be expected to make it to the SCOTUS docket earlier in our republic.