Why?
To make it easier for us non-native English speakers to learn *hehe*
Unlike Dutch, where you need to learn
jij, jullie and U
--> the U tends to get lost, too, right?! It's nearly vanished in Scandinavian languages already.
In German, all three forms are still used for addressing:
du (you, sg.), ihr (you, pl.) and Sie (polite you, sg and pl).
In old literature and films setting around the middle ages, also "Ihr" (you, pl.) is used instead of Sie (polite you, sg, pl) to be the polite form of addressing, also for a single person. "Er/sie" (he/she) can be found in addition as a pronoun for addressing people in older language.
For the Majestatis Pluralis, "Wir" (we) is used instead of ich (I). ;-)