That is my question. The Supremes can only decide if something is constitutional. The PEOPLE just decided that the constitution says that same sex couples can not be legally married. That’s it. Supremes can not change the constitution....only the people can.
IOW... they can't really say "we overturn the amendment", but they think they can say "you didn't actually amend it". A federal court could (at least in theory) say "that conflicts with the federal constitution and cannot be enforced" (just as if a state constitution banned abortion... it would still be in the constitution, but would be held invalid).
That's worked before, but looks set to fail here. One of the supporters of gay "marriage" on the court wasn't even willing to review the challenge... she only wanted to decide whether existing "marriages" were invalid given the amendment.