I think it might be a symptom of my self-involvement. Unless something impacts me directly I tend not to notice.In fact, sometimes I don't even notice when it does impact me directly. I tend to forget things like my birthday because it's not really relevant to whatever else is going on in my head. In fact, if someone were to ask how old I am, I wouldn't be able to say without counting.
I guess what this really amounts to is an excuse for being lazy.