The Arcane Archer is a perfect example of why every member of a class would have access to the same set of abilities. If you want to learn how to launch a Cone of Cold from your arrow, then you need to belong to one specific organization of elvish archers, where they teach you. Otherwise, that specific knowledge is unavailable. And if you do belong to that organization, then they have a standard set of tricks that they teach all of their members.
Other classes are similar. If you want to be a Cleric of Wee Jas, or an Eldritch Knight, then you belong to an organization where they teach you a standard set of tricks. It's just a thing about how the setting works. For generic classes, like Fighter, there are a lot of different organizations that get you to a similar-looking endpoint. And while I suppose you could play in some other setting, where you don't learn your class abilities from an organization, such a setting would really be better represented with a non-class-based system.