You're operating with the underlying assumption that if corner crossing was clarified by SCOTUS, it would require "giving up a right." That assumption is simply not true.
Advocates in favor of clarifying the issue, myself included (some of us aren't just armchair lawyers), aren't operating under that assumption. We're asking for BLM, SCOTUS, USFS, and everyone else to recognize a right we, as public taxpayers, already have: a right to access land we own.
We come from a position that, for far too long, some landowners have been operating as though they "have a right" to landlock public land. That assumption hasn't been clarified by anyone, although the WY decision went a long ways to undercut it, and relies on some pretty sound logic to get there.
As an aside, many landowners, even when given a plethora of options (be it public access agreements, damage hunts, etc) choose to act as though their rights are being infringed and they are somehow being punished or "forced" to do something they should have been doing in the first place, instead of recognizing that they don't have a leg to stand on. Nobody is treading on their rights. These are public lands, and public resources, and the public's rights are the ones being infringed.
The only thing we are asking these people to "give up" is the misguided notion that they are entitled to something that was never theirs in the first place, which is a far cry from a "right."