Why do most RPGs, even "narrative" ones like Fate and Dungeon World, have you roll for knowledge/lore skills?

How does this make sense? You either know something or you do not. Where does chance figure into the equation? Rolls are more riveting when something interesting happens even on a failed roll ("fail forward"), yet it tends to be hard to come up with interesting things for failed knowledge rolls other than a clue on where to find the information.

Chance could make sense when trying to remember something while in a very stressful situation like combat, but otherwise, why is a roll even happening?

The knowledge system I like most is that of Legends of the Wulin. The game's setting lists down "loresheets" regarding many different facets of the game world that you can spend points to purchase. If you purchase a loresheet, then your character knows about that topic, no questions asked, unless the topic is incredibly obscure even for that loresheet (in which case you get to questing). You do have a general knowledge skill, but this is purely for general knowledge, combat skill use, and special abilities; you never roll it to know about town X, historical event Y, or faction Z, because that is the job of loresheets.

What RPGs have rules for in-character knowledge that you particularly like?