But what would make them so corrupt? I mean they were so friendly in every other game
Look at it...
1. Zoras lived in wonderful Hyrule.
2. Hyrule is flooded.
3. The Zoras magically evolved into the Rito (WW).
4. The River Zoras (Zolas) appear, perhaps also as evolutions, or as another species altogether.
5. The Rito remain on Dragon Roost Island while the River Zoras, brute beings, are able to swim the expanses of the sea, eventually settling in the rivers of scattered islands (PH) if they weren't native to the islands in PH's Great Sea already (which could very well be their origins).
6. The River Zora species makes it way to the land that becomes New Hyrule, being renamed the Geozard species (land-lizard), effectively and finally properly dubbing the species apart from the Zora.
So the prominent races we have are:
- Human
- Hylian
- Sheikah
- Gerudo
- Twili
- Goron
- Zora
- Rito
- Geozard
- Deku
- Kokiri
- Korok
- Minish
- Anouki
- Yeti
Note: the names River Zora and Sea Zora come from OoA. Because both types of Zoras were present in the game, those popularized by OoT/MM lived in the sea (thus Sea Zora), and those from the older games lived in rivers (thus River Zora).