Assuming empathy is a worldly thing (which i believe it is), why does/would a buddha try to help others find the way?

I've always believed that empathy/feeling for others is a biological feature of evolution in social animals. So, why does/would an enlightened being go to lengths to help others reach enlightenment? Maybe if we are all different instances of the same consciousness, it kind of makes a little sense (one enlightened instance helping others),but not completely. Could someone clarify?