Here's what it comes down to:
People that in general that watch anime look for things that instantly gratify you. They will look for battles, girls, blood, and shiny things. That is basically what most anime is.
However, eva has these things, but it has one extra side: it's designed to make you actually think. This is a uncommon and rare thing in anime that even when it's there, it goes unnoticed. So to the people of /a/, all of that time that you were supposed to be thinking, listening, and watching carefully: that was all just wasted airtime.
To /a/, anime isn't supposed to make you think. It's only supposed to make your penis hard. When they see Rei and Asuka, they don't see Shinji being torn apart by opposite personalities trying to fill in the blankspots of his life, they see a hotheaded german girl and a quiet and shy albino. The former is clearly there, however, they choose not to look for it.
This process occurs time and time again while those people who are watching eva while looking for what is unimportant.