Right. But the trick is getting it that first time. Xûr sold the Gjallarhorn in like, the first month of Destiny 1, and then never again (or at least for as long as I played).
I don’t know exactly how the loot tables worked behind the scenes, but it remained very elusive for people who missed it.
People ran every nightfall and raid they could and still came up empty. So everyone’s worried they’ll overlook something again that turns out to be useful after they passed on the opportunity to grab it.