An agency acting on issues with staggering economic and political significance requires explicit authorization from Congress.
When an executive action is struck down under the Major Questions Doctrine, it does not invalidate the entire statute; rather, only the executive action is struck down.
From this case: The HEROES Act allowed the Secretary of Education to "waive or modify" certain provisions of student financial assistance. The provision did not allow for the cancellation of $430 billion in student loans. This was a major question, and Congress did not explicitly dive this authority.
J. Barrett's concurrence:
MQD is an interpretive tool reflecting the idea of common sense.
Does giving the babysitter the credit card and saying "have fun" mean she can take the kids on a two-day camping trip? No.
Thus, Congress keeps big (major questions) decisions for themselves unless explicitly delegated.
Summation: Court assumes that Congress didn't mean to give away a massive amount of power that it did not explicitly grant.
The Statute survives, but the agency action doesn't.