Silva lost his 3rd mma fight, he wasn't undefeated.
I think certain guys have a different mystique. Khabib is undefeated and no one he fought came close. GSP has lost, Woodley has lost, Silva has lost, etc... well before their expiry date.
Khabib also left at a relatively young age. GSP losing tomorrow isn't the same as Khabib losing tomorrow.
Woodley was never some super GOAT status fighter. Losing at 39(soon to be 40) doesn't scream "OH NO HIS LEGACY". I shrug, I know he's just over the hill and should retire.
The same was Belfort beat Hollyfield. I doubt any boxing fan says "wow...that mystique is damaged." They probably just think Hollyfield shouldn't fight anymore. Same with Woodley.
As for Silva, he's prolonging the inevitable. He's boxing recently and doing okay but he's going to fight someone who is younger, more durable and will make him look like a fool. Does it hurt his legacy? Nah, he's 47 in april but it does make him look foolish for not stopping. Same with woodley.
As for GSP, Khabib and guys like that. Few guys leave on top. What they did is rare, not the norm.