It fit better with the overall design.
Green is a more positive color.
It was a superior icon, but people on here are obviously afraid of change. It's quite normal, really.
I like this one better, the new one was too neutral. This one has an element of intensity, when you log in and see that thing lit up, it could be anything. That exclamation mark made you think about everything youve said on here for the past week before you click on it, just so you have an idea of what you were getting yourself into. This notification asks you, "hey did you check yourself? Click me to see if you wrecked yourself."