Google doesn’t understand social or collaboration. There’s not much more to it than that, though for the sake of making this a an actual blog post I’ll explain a bit more.
Blogger was huge, it was the place to go if you were creating a blog. There weren’t many www.mybloghere.com, many of the largest most popular blogs on the internet were on blogger. People had accounts, people registered to post comments, people had full fledged profiles that could have easily preceded a facebook profile page. Google bought blogger and had more than enough resources to grow blogger into a sizable social community. But if you visit it looks much the same as it did 5 and almost 10 years ago.