This can happen because certain key cards that countered them have rotated out, or because new card combinations become viable
At the same time, spells like Call of the Death-Dweller and Agadeems Awakening can resurrect creatures from the graveyard
The legendary permanent you get rid of will "die" but the legend rule also ignores the indestructible keyword
After all that, Sauron will mostly just be a 9/9 beater, though it also has the Ring's temptation anytime an opponent's commander dies
The reasoning behind this may be because by default, you can't Tribute your opponent's cards, so there would be no reason to say it, unless of course you want to Tribute the opponent's monsters as well
If you have like a card thats got a seagull on it, like Im thinking about the Vexing Gull, as a Magic player, you could probably intuit off the top of your head that, since its a seagull, it might be like a one or two cost white or blue card, likely with Flying, and then it might have like some sort of ability that summons other Gulls next to it or whatever, because its a seagull and thats what it does