Because of the fel corruption. But Kael'thas renamed his people to Blood Elves before they were dealing with any kind of fel. So all High Elves from that point on were called Blood Elves, green eyes or blue eyes, doesn't matter.
Sorry, bra, but I do know the lore.
Blood Elves wasn't a name that was chosen because of any fel corruption. It was a name to honor the hardships of his people. The blood that was spilled. If he renamed them because of the fel corruption he would've called them Fel Elves.