Because the High Elves have never been depicted as anything other than Blood Elves with blue eyes. Unlike the Kul Tirans who were never featured since Warcraft III and thus allowed a lot of creative freedom for the writers.
Also, I love how OP berated the Kul Tirans by calling them “Fat Humans”, while ignoring the fact that they are the most unique and complex Allied Race by far. Much better than purple Blood Elves, uglier Night Elves, Tauren with different horns, and Draenei with a lighter skin tone.
Because let’s be real, the only reason why Kul Tirans are not played that much is because they remind a lot of players of what they are in real life, even more so than normal Humans. If people chose their race based on their background and complexity, the Kul Tirans would be the most played Allied Race by far.