re: Another day...another Obama appointed judge reversing a Trump policy

Because changes in administrative law are based on whether or not the administration’s interpretation of the law is reasonable. If the interpretation being offered by a new administrator is remarkably different, then they will have to either prove:
A. That their interpretation is reasonable because that’s what the drafters meant it to mean; or
B. That research and data supports changing the interpretation to what the new administration desires, i.e. that it’s reasonable policy.

Thus, big changes are typically frowned upon by judges.