One big reason I care about who wrote things is expertise. Ex: I've consistently seen informed and sensible security-related commentary from tptacek, so I would pay more attention to security-related advice with his name on it than if it was a name I didn't recognize.
I guess it wouldn't if one didn't value people. YMMV, but I think people are kind of cool — so if I hear a great song I want to know who the artist was. It helps me build a mental model of what I might be able to expect from them. I'm kind of shocked that this might not be obvious to everyone, TBH.
I wonder how many people have that reflex. I usually only notice usernames when mentioned by others.